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energy, an electron can be removed from an atom and be freed from its
attraction to the nucleus.
Atomic nucleus
A model of the atomic nucleus showing it as a compact bundle of the two
types of nucleons: protons (red) and neutrons (blue). In this diagram, protons
and neutrons look like little balls stuck together, but an
actual nucleus (as understood by modern nuclear physics)
cannot be explained like this, but only by using quantum
mechanics. In a nucleus which occupies a certain energy
level (for example, the ground state), each nucleon has
multiple locations at once.
The nucleus is the very dense region consisting of protons and neutrons at
the center of an atom. It was discovered in 1911 as a result of Ernest
Rutherford's interpretation of the 1909 Geiger–Marsden gold foil experiment
performed by Hans Geiger and Ernest Marsden under Rutherford's direction.
The proton–neutron model of nucleus was proposed by Dmitry Ivanenko in
1932.[1]
Almost all of the mass of an atom is located in the nucleus, with a
very small contribution from the electron cloud.
The diameter of the nucleus is in the range of 1.75 fm (1.75×10−15
m)
for hydrogen (the diameter of a single proton)[2][not in citation given]
to about 15 fm
for the heaviest atoms, such as uranium. These dimensions are much smaller
than the diameter of the atom itself (nucleus + electron cloud), by a factor of
about 23,000 (uranium) to about 145,000 (hydrogen).](https://image.slidesharecdn.com/bahanajarrevisi-140123041220-phpapp01/85/Bahan-ajar-listrik-statis-english-version-20-320.jpg)
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S is any closed surface,
Q is the total electric charge inside the surface S,
ε0 is the electric constant (a universal constant, also called the "permittivity of
free space") (ε0 ≈ 8.854 187 817... x 10−12
farads per meter (F·m−1
)).
This relation is known as Gauss' law for electric field in its integral form and
it is one of the four Maxwell's equations.
It is important to note that while the electric flux is not affected by
charges that are not within the closed surface, the net electric field, E, in the
Gauss' Law equation, can be affected by charges that lie outside the closed
surface. While Gauss' Law holds for all situations, it is only useful for "by
hand" calculations when high degrees of symmetry exist in the electric field.
Examples include spherical and cylindrical symmetry.
Electrical flux has SI units of volt metres (V m), or, equivalently,
newton metres squared per coulomb (N m2
C−1
). Thus, the SI base units of
electric flux are kg·m3
·s−3
·A−1
.
Its dimensional formula is [L3
MT–1
I–1
].
6.3 Summary
1. The electric flux through an area is defined as the electric field multiplied by
the area of the surface projected in a plane perpendicular to the field.
2. The concept of electric flux is useful in association with Gauss' law.
3. The electric flux through a planar area is defined as the electric field times the
component of the area perpendicular to the field.
6.4 Exercise
1. Electeric flux are defined ....
2. The equation of electric flux is ....
3. Electric flux SI units is ....
4. The dimensional formula for electric flux is ....
5. This relation is known as .... for electric field in its integral form and it is one
of the four Maxwell's equations
6.5 Formative Test](https://image.slidesharecdn.com/bahanajarrevisi-140123041220-phpapp01/85/Bahan-ajar-listrik-statis-english-version-60-320.jpg)
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Gaussian surface of radius R. The sphere’s center lies on the wire. Located
outside the sphere is another charge +q. What is the total electric flux through
the sphere?
6.6 Answer Key
Exercise answer key
1. as the electric field multiplied by the area of the surface projected in a
plane perpendicular to the field
2.
3. volt metres (V m), or, equivalently, newton metres squared per coulomb
(N m2
C−1
). Thus, the SI base units of electric flux are kg·m3
·s−3
·A−1
.
4. Its dimensional formula is [L3
MT–1
I–1
].
5. Gauss’s Law
Formative answer key
1. A
2. D
3. B
4. A
5. D
6.7 Student Worksheet
Title : Electric Flux
Lesson : Natural Science
Semester : 2
Location : Classroom
Learning Instruction : Learn the material about electric flux
Competence : Understanding the concept of electric flux
Indicators : Students can using the concept of electric for answer the
problem.
Information :
Assignments : Read and answer the question below!
A field of 500 cm2 exposed to strong homogeneous electric field with the angle
of arrival](https://image.slidesharecdn.com/bahanajarrevisi-140123041220-phpapp01/85/Bahan-ajar-listrik-statis-english-version-62-320.jpg)
Uploaded bykhairul jalil
Bahan ajar listrik statis (english version)
1. The document is a physics textbook for 9th grade junior high school students covering the topic of static electricity. It includes 7 learning activities on key concepts such as atom, electric charge, Coulomb's law, electric force, electric field, electric flux, and electric potential. 2. Each learning activity includes the learning strategy, concept explanation, summary, exercises, formative test, answer key, and student worksheet. Concepts are explained through examples and illustrations. Formative assessments are used to check students' understanding. 3. The goal is for students to understand concepts of static electricity including electric charge, electric potential, electric current, electrostatics in the nervous system, and examples in animals that contain electricity
Bahan ajar listrik statis (english version)
- 1. PHYSICSfor 9 gradeJunior High School STATIC ELECTRICITY Erlin Eveline Khairul Jalil Reni Oktafia
- 2. i PREFACE Gratitude belongs onlyto Almighty Allah, who has given his affection to the author for taking the time to complete the paper titled " Bahan Ajar Fisika materi Static Electric. for a tast intructional physics in Semester 3rd . The authors also thank those who have assisted in the completion of this paper. The authors are aware that this paper is still far from perfect. Therefore, the authors expect criticism and suggestions either in writing or orally, in particular course to the Intructional Physics lecturer, Dra. Haratua Tiur Maria S. M.Pd and Erwina Oktavianty M.Pd, so that writers can develop science, especially science Intructional Physics. And thanks to all reader this paper. December 22th, 2013 Writer
- 3. ii TABLE OF CONTENT ANDFRAMEWORK STATIC ELECTRICITY Preface....................................................................................................................................i Table of Content.....................................................................................................................ii Mind Map...............................................................................................................................iii Sylabus...................................................................................................................................iv Analyse of Physics Concept...................................................................................................v INTRODUCTION................................................................................................................. 1 A. Description.................................................................................................................1 B. Modul Instruction.......................................................................................................1 D. Studying Purpose....................................................................................................... 2 E. Content Competence..................................................................................................2 F. Basic Competence......................................................................................................2 G. Indicator..................................................................................................................... 3 LEARNING........................................................................................................................... 4 A. Learning Plan............................................................................................................. 4 B. Studying Activity.......................................................................................................4 1. Studying activity 1 : ATOM............................................................................... 4 1.1.......................................................................................................................Lea rning Strategy4 1.2.......................................................................................................................Ato m...................................................................................................................4 1.3.......................................................................................................................Su mmary.......................................................................................................... 12 1.4.......................................................................................................................Exe rcise .............................................................................................................13
- 4. ii 1.5.......................................................................................................................For mative Test ..................................................................................................13 1.6.......................................................................................................................An swerKey...................................................................................................... 14 1.7.......................................................................................................................Stu dent Worksheet ........................................................................................... 14 2. Studying Activity 2 : ELECTRIC CHARGE..................................................... 15 2.1........................................................................................................................Lea rning Strategy................................................................................................15 2.2........................................................................................................................Ele ctric Charge...................................................................................................15 2.3........................................................................................................................Su mmary........................................................................................................... 19 2.4........................................................................................................................Exe rcise............................................................................................................... 19 2.5........................................................................................................................For mative Test ...................................................................................................20 2.6........................................................................................................................An swer Key....................................................................................................... 21 2.7........................................................................................................................Stu dent Worksheet .............................................................................................21 3. Studying Activity 3 : COULOMB LAW............................................................22 3.1........................................................................................................................Lea rning Strategy................................................................................................22 3.2........................................................................................................................Co ulomb Law.................................................................................................... 22 3.3........................................................................................................................Su mmary........................................................................................................... 24 3.4........................................................................................................................Exe rcise............................................................................................................... 25 3.5........................................................................................................................For mative Test ...................................................................................................25 3.6........................................................................................................................An swer Key....................................................................................................... 26
- 5. ii 3.7........................................................................................................................Stu dent Worksheet .............................................................................................27 4.Studying Activity 3 : ELECTRIC FORCE.........................................................27 4.1........................................................................................................................Lea rning Strategy................................................................................................27 4.2........................................................................................................................Ele ctric Force......................................................................................................27 4.3........................................................................................................................Su mmary........................................................................................................... 31 4.4........................................................................................................................Exe rcise............................................................................................................... 32 4.5........................................................................................................................For mative Test ...................................................................................................32 4.6........................................................................................................................An swer Key....................................................................................................... 33 4.7........................................................................................................................Stu dent Worksheet..............................................................................................33 5. Studying Activity 5 : ELECTRIC FIELD...........................................................34 5.1........................................................................................................................Lea rning Strategy................................................................................................34 5.2........................................................................................................................Ele ctric Field...................................................................................................... 34 5.3........................................................................................................................Su mmary........................................................................................................... 42 5.4........................................................................................................................Exe rcise............................................................................................................... 42 5.5........................................................................................................................For mative Test ...................................................................................................42 5.6........................................................................................................................An swer Key....................................................................................................... 43 5.7........................................................................................................................Stu dent Worksheet..............................................................................................44 6. Studying Activity : ELECTRIC FLUX.............................................................. 44
- 6. ii 6.1........................................................................................................................Lea rning Strategy................................................................................................44 6.2........................................................................................................................Ele ctric Flux.......................................................................................................44 6.3........................................................................................................................Su mmary........................................................................................................... 47 6.4........................................................................................................................Exe rcise............................................................................................................... 47 6.5........................................................................................................................For mative Test ...................................................................................................47 6.6........................................................................................................................An swer Key....................................................................................................... 48 6.7........................................................................................................................Stu dent Worksheet..............................................................................................49 7. Studying Activity 7 : ELECTRIC POTENTIAL................................................49 7.1........................................................................................................................Lea rning Strategy................................................................................................49 7.2........................................................................................................................Ele ctric Potential................................................................................................ 50 7.3........................................................................................................................Su mmary........................................................................................................... 53 7.4........................................................................................................................Exe rcise............................................................................................................... 53 7.5........................................................................................................................For mative Test ...................................................................................................53 7.6........................................................................................................................An swer Key....................................................................................................... 54 7.7........................................................................................................................Stu dent Worksheet..............................................................................................55 EVALUATION......................................................................................................................56 BIBLIOGRAFI
- 7.
- 8. iv SILABUS MATA PELAJARAN: IPA SatuanPendidikan : SMP Kelas /Semester: IX Kompetensi Inti* KI 1 : KI 2 : KI 3 : KI 4 : Kompetensi Dasar Materi Pokok Pembelajaran Penilaian Alokasi Waktu Sumber Belajar Listrik Statis Mengamati Peristiwa sehari-hari yang berhubungan dengan listrik statis, misalnya penggaris plastik yang telah digosok, dapat menarik kertas yang disobek kecil-kecil. Menanya Diskusi tentang: 1. Gejala listrik pada benda 2. Gaya listrik 3. Prinsip kerja elektroskop Eksperimen/explore 1. Gejala listrik pada benda (penggaris plastik yang bersih atau masih baru, kaca, kain sutra, kain wol, kertas yang di sobek kecil- kecil) Tugas 1. Membuat tulisan tentang hubungan antara listrik statis dengan terjadinya petir dan cara menanggulangi agar tidak tersambar petir 2. Diskusi kelompok membahas hasil eksperimen listrik statis 3. Membuat laporan eksperimen listrik statis Observasi Mengamati kegiatan eksperimen dan menilainya dengan menggunakan rubrik. Portofolio 1 x 5 JP Buku paket, Lembar kerja Praktikum Buku atau sumber belajar yang relevan. Media elektronik 3.5 Memahami konsep listrik statis, muatan listrik, potensial listrik, hantaran listrik, kelistrikan pada sistem syaraf, dan contohnya pada hewan-hewan yang mengandung listrik Menghargai dan menghayati ajaran agama yang dianutnya. Menghargai dan menghayati perilaku jujur, disiplin, tanggungjawab, peduli (toleransi, gotong royong), santun, percaya diri, dalam berinteraksi secara efektif dengan lingkungan sosial dan alam dalam jangkauan pergaulan dan keberadaannya. Memahami dan menerapkan pengetahuan (faktual, konseptual, dan prosedural) berdasarkan rasa ingin tahunya tentang ilmu pengetahuan, teknologi, seni, budaya terkait fenomena dan kejadian tampak mata. Mengolah, menyaji, dan menalar dalam ranah konkret (menggunakan, mengurai, merangkai, memodifikasi, dan membuat) dan ranah abstrak (menulis, membaca, menghitung, menggambar, dan mengarang) sesuai dengan yang dipelajari di sekolah dan sumber lain yang sama dalam sudut pandang/teori.
- 9. iv Kompetensi Dasar MateriPokok Pembelajaran Penilaian Alokasi Waktu Sumber Belajar 2. Gaya akibat muatan listrik (penggaris plastik yang bersih atau masih baru 2 buah 2 buah , kaca, kain sutra 2 helai, kain wol 2 helai, benang dan statif masing-masing 1 buah) 3. Prinsip kerja elektroskop Asosiasi 1. Menganalisis data untuk mendapakan konsep gejala listrik 2. Menganalisis data untuk mendapatkan sifat- sifat muatan listrik Komunikasi 1. Membuat laporaneksperimen tertulis 2. Mempresentasikan hasil eksperimen Kumpulan: 1. Laporan tertulis kelompok hasil eksperimen 2. Laporan (tulisan) tentang terjadinya petir dan upaya menghindari sambaran petir. Tes Tulis Contoh PG Sepotong Kaca akan bermuatan listrik positif bila digosok dengan kain sutera karena .... a. elektron dari kaca pindah ke sutera b. proton dari kaca pindah ke sutera c. elektron dari sutera pindah ke kaca d. proton dari sutera pindah ke kaca Uraian Jelaskan dan gambar prinsip kerja elektroskop yang digunakan untuk mengetahui apakah sebuah benda bermuatan listrik atau tidak.
- 10. v Satuan Pendidikan :SMP Kelas /Semester : IX Kompetensi Inti* KI 1 : KI 2 : KI 3 : KI 4 : Kompetensi Dasar : Memahami konsep listrik statis, muatan listrik, potensial listrik, hantaran listrik, kelistrikan pada system syaraf, dan contohnya pada hewan-hewan yang mengandung listrik No Konsep Atribut Posisi Contoh Noncontoh Label Jenis Definisi Kritis Variabel Super- ordinat Koo rdin at Sub- ordinat 1 Muatan Listrik Abstrak Muatan dasar yang dimiliki suatu benda yang membuatnya mengalami gaya pada benda lain yang berdekatan dan juga memiliki muatan listrik Muatan listrik, partikel, materi Besar, jenis muatan Benda - - Ion positif, ion negatif Interaksi antara Rambut dan sisir menghasilkan muatan listrik 2 Atom Abstrak Atom merupakan bagian terkecil dari suatu materi Partikel terkecil, inti atom dan kulit atom Jari-jari inti atom, jenis atom (proton, neutron, Materi Inti atom Proton, elektron, neutron Atom hidrogen Proton, neutron, elektron Menghargaidanmenghayatiajaran agama yang dianutnya. Menghargai dan menghayati perilaku jujur, disiplin, tanggungjawab, peduli (toleransi, gotong royong), santun, percaya diri, dalam berinteraksi secara efektif dengan lingkungan sosial dan alam dalam jangkauan pergaulan dan keberadaannya. Memahamidanmenerapkanpengetahuan (faktual, konseptual, danprosedural) berdasarkan rasa ingintahunyatentangilmupengetahuan, teknologi, seni, budayaterkaitfenomenadankejadiantampakmata. Mengolah, menyaji, danmenalardalamranahkonkret (menggunakan, mengurai, merangkai, memodifikasi, danmembuat) danranahabstrak (menulis, membaca, menghitung, menggambar, danmengarang) sesuaidengan yang dipelajari di sekolahdansumber lain yang samadalamsudutpandang/teori.
- 11. v elektron) 3 Hukum Coulom b Berda sarkan Prinsi p Hukum yang menjelaskanhubungan antara gaya yang ditimbulkan antara dua titik muatan, yang terpisahkan dengan jarak tertentu dengan nilai muatan dan jarak pisah keduanya Hukum Coulomb, besar gaya coulomb, jarak antara keduamuat an listik Besargaya coulomb, besar jarak kedua muatan listrik, besar muatan, arah gaya Gaya listrik - Medan listrik Muatanlistrik +q3=20 µC, +q2=µC, dan q1terpisah seperti pada gambar .tentukan muatan q1 agar gaya coulomb yang bekerja pada muatan q2=0. 4 Gaya Listrik Abstra k Gaya yang dialami oleh objek bermuatan yang berada dalam medan listrik Gaya listrik, benda bermuatan, medan listrik Arah gaya listrik, besar gaya listrik, jenis muatan, jarak antar muatan Gaya - Gaya listrik Interaksi dua muatan Penggaris plastik yang digosokkan wol dapat menarik potongan kertas ringan 5 Medan listrik Abstra k Ruang atau daerah yang masih dipengaruhi gaya listrik Medan listrik, ruang disekitarm uatan listrik, gaya coulomb, muatan sumber Kuat medan listrik, besa rmuatan uji, gaya yang dialami muatan uji, arah medan listrik Gaya listrik Kuat med anlis trik Hukum Gauss Kuat medan listrik diantara dua muatan pada jarak tertentu Muatan q dan 2q terpisahsejauh r berinteraksimenghas ilkanmedanlistrik 6 Fluks listrik Abstra k Jumlah garis-garis medan yang menembus suatu bidang, hasil kali antara kuat medan listrik E dengan luas bidang A medan listrik tersebut Fluks listrik, kuat medan listrik, luas bidang, sudut antara E dengan Luas bidang, kuat medan listrik, sudut antara E dengan garis normal Garis- garism edan - Hukum gauss Tentukan fluks listrik yang garis-garis gaya menembus tegak lurus bidang jika diketahui garis-garis gaya magnetik seragam dengan kerapatan 150 menembus bidang Garis-garis gaya yang menembus tegak lurus bidang tertentu
- 12. v garis normal seluas 100 cm2 . 7Potensi al Listrik Abstra k Potensial merupakan energi potensial listrik per satuan waktu Potensial listrik, energi potensial listrik, muatan listrik Jenis muatan, jarak antar muatan Energi potensi al listrik Potensial listrik dari sebuah titik yang berjarak r dan muatan titik Q adalah Arah potensial listrik pada sebuah titik berjarak r dan muatan titik q
- 13. 1 INTRODUCTION A. Description B. ModulInstructions For students : 1. Read the learning plan 2. Read the learning strategy for understand the way how you learn 3. Study the content and answer the question to know the improve of yours understanding. For teacher : 1. Read the learning plan 2. Read the learning strategy for understand the way how the teaching 3. Study the content before teaching in class. In physics the term of electric is classified in two types, that are static electric and dynamic electric. The static electric learns about the nature of body electricity without mention the electric charge motion or its flows. In physics it called the electrostatic. Inversly if is mentioned to its motion or flows it called electrodynamic. The electromagnetic force between charged particles is one of the fundamental forces of nature. We begin this chapter by describing some of the basic properties of one manifestation of the electromagnetic force, the electric force. We then discuss Coulomb’s law, which is the fundamental law governing the electric force between any two charged particles. Next, we introduce the concept of an electric field associated with a charge distribution and describe its effect on other charged particles. We then show how to use Coulomb’s law to calculate the electric field for a given charge distribution. We conclude the chapter with a discussion of the motion of a charged particle in a uniform electric field. This book has a learning material, example, and question which can help student understanding the lesson.
- 14. 2 C. Studying Purpose D.Content Competence E. Basic Competence Students can Mention type of electric charge Students can give examples of phenomenon that produce electrically charged objects Students can explain the function of the electroscope, coulomb law, and electric potential Students can explain the objects can have electrical charge if we did that objects in a one or more way. Student can perform a simple experiment to demonstrate the characteristic of electric charge Student can describe qualitatively the relationship between electric force and electric charge and the distance between electrical charge of objects K1: Appreciate and comprehend fully religion doctrine who they faith. K2: Appreciate and comprehend fully honest behavior, discipline behavior, responsible behavior, care behavior (tolerance, help together), well behaved, confidence, in interactions effectively with social environment/area and nature in society range and their existance, K3: Knowledge understanding and applying (factual, conceptual, and procedural) which building on their curiosity about knowledge, technology, art, culture concerned phenomenon and accurence that we can see. K4: Processing, Presenting, and thinking in concrete domain (using, explain, rafting, modification, and making) and abstract domain (writing, reading, counting, drawing, arranging) which agree with lessons in schools and the others source that same with point of view/theory. 3.5 Understanding of static electric concept, electric field, electric potential, electric bring, electricity of nerves system, and example of static electric at animals who have within it electricity.
- 15. 3 F. Indicator Mentiontype of electric charge Give examples of phenomenon that produce electrically charged objects Explain the function of the electroscope, coulomb law, and electric potential Explain the objects can have electrical charge if we did that objects in a one or more way. Perform a simple experiment to demonstrate the characteristic of electric charge Describe qualitatively the relationship between electric force and electric charge and the distance between electrical charge of objects
- 16. 4 LEARNING A. Learning Plan 1)In learning this moduls, you will use inquiry approach. Inquiry based approaches to education focus on student constructed learning as opposed to teacher-transmitted information. Inquiry learning is an intriguing and exciting way to teach. It involves students as active learners, learning real life skills. Traditional student and teacher roles are changed to a collaborative relationship rather than the “sage on the stage” approach. Inquiry learning is very adaptable and can be used to different extents depending on desired learning outcomes. 2) Teacher guide you to learn one by one of materials. Then, teacher will give some exercise or homework to know your understanding about the materials. 3) Teacher make some groups from you are. You will have an group in class and learn together with your group. 4) In the end of this lesson, you will have test to know the result everyone of you. 5) Guiding Question: The goal of your lesson should be inquiry oriented. Students’ attention should be focused on answering questions based on empirical evidence. Remember that teacher simply asking lots of questions does not an inquiry lesson make. 6) Student Performance Objective: What, more specifically, are the students expected to know and be able to do at the end of the lesson? Include content knowledge, intellectual skills, and dispositions as appropriate. Your objectives should have readily observable behaviors or performance tasks. Students must be made aware of day-to- day objectives. 7) Instructional Approach: Indicate which active learning strategies you will employ in this inquiry lesson such as discovery learning, interactive demonstration, inquiry lesson, inquiry lab, hypothetical inquiry, problem/project based learning, case study, discussion, etc. Good inquiry-oriented lessons also will include activities from each of the three following categories: individualized, small group, and whole group. B. Studying Activity 1. Studying Activity 1 : ATOM 1.1 Learning Strategy 1) Use the drill learning method
- 17. 5 Drill learning methodis a method that you always repeat what you learn with give you many exercise. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills. 1.2 Atom a. Introduction What are atoms? Atoms are the basic building blocks of matter that make up everyday objects. A desk, the air, even you are made up of atoms! There are 90 naturally occurring kinds of atoms. Scientists in labs have been able to make about 25 more. The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. (Leigh, G. J., ed. (1990). b. Content Atoms and Elements Ordinary matter is made up of protons, neutrons, and electrons and is composed of atoms. An atom consists of a tiny nucleus made up of protons and neutrons, on the order of 20,000 times smaller than the size of the atom. The outer part of the atom consists of a number of electrons equal to the number of protons, making the normal atom electrically neutral. A chemical element consists of those atoms with a specific number of protons in the nucleus; this number is called the atomic number. The atoms of an element may differ in the number of neutrons; atoms with different neutron numbers are said to be different isotopes of the element. Elements are represented by a chemical symbol, with the atomic number and mass number sometimes affixed as indicated below. The mass number is the sum of the numbers of neutrons and protons in the nucleus.
- 18. 6 The elements canbe identified unambiguously by the "spectral fingerprints" of their line spectra and in some cases by the flame colors given off by excited atoms. History of Atomic Structure The early Greeks were simply philosophers. They did not perform experiments to test their theories. In fact, science as an experimental discipline did not emerge as a credible and popular practice until sometime during the 1600s. So the search for the atom remained a philosophical inquiry for a couple of millennia. From the 1600s to the present century, the search for the atom became an experimental pursuit. Several scientists are notable; among them are Robert Boyle, John Dalton, J.J. Thomson, Ernest Rutherford, and Neils Bohr. Boyle's studies (middle to late 1600s) of gaseous substances promoted the idea that there were different types of atoms known as elements. Dalton (early 1800s) conducted a variety of experiments to show that different elements can combine in fixed ratios of masses to form compounds. Dalton subsequently proposed one of the first theories of atomic behavior that was supported by actual experimental evidence. English scientist J.J. Thomson's cathode ray experiments (end of the 19th century) led to the discovery of the negatively charged electron and the first ideas of the structure of these indivisible atoms. Thomson proposed the Plum Pudding Model, suggesting that an atom's structure resembles the favorite English dessert - plum pudding. The raisins dispersed amidst the plum pudding are analogous to negatively charged electrons immersed in a sea of positive charge. Nearly a decade after Thomson, Ernest Rutherford's famous gold foil experiments led to the nuclear model of atomic structure. Rutherford's model suggested that the atom consisted of a densely packed core of positive charge known as the nucleus surrounded by negatively charged electrons. While the nucleus was unique to the Rutherford atom, even more surprising
- 19. 7 was the proposalthat an atom consisted mostly of empty space. Most the mass was packed into the nucleus that was abnormally small compared to the actual size of the atom. Neils Bohr improved upon Rutherford's nuclear model (1913) by explaining that the electrons were present in orbits outside the nucleus. The electrons were confined to specific orbits of fixed radius, each characterized by their own discrete levels of energy. While electrons could be forced from one orbit to another orbit, it could never occupy the space between orbits. Bohr's view of quantized energy levels was the precursor to modern quantum mechanical views of the atoms. The mathematical nature of quantum mechanics prohibits a discussion of its details and restricts us to a brief conceptual description of its features. Quantum mechanics suggests that an atom is composed of a variety of subatomic particles. The three main subatomic particles are the proton, electron and neutron. The proton and neutron are the most massive of the three subatomic particles; they are located in the nucleus of the atom, forming the dense core of the atom. The proton is charged positively. The neutron does not possess a charge and is said to be neutral. The protons and neutrons are bound tightly together within the nucleus of the atom. Outside the nucleus are concentric spherical regions of space known as electron shells. The shells are the home of the negatively charged electrons. Each shell is characterized by a distinct energy level. Outer shells have higher energy levels and are characterized as being lower in stability. Electrons in higher energy shells can move down to lower energy shells; this movement is accompanied by the release of energy. Similarly, electrons in lower energy shells can be induced to move to the higher energy outer shells by the addition of energy to the atom. If provided sufficient
- 20. 8 energy, an electroncan be removed from an atom and be freed from its attraction to the nucleus. Atomic nucleus A model of the atomic nucleus showing it as a compact bundle of the two types of nucleons: protons (red) and neutrons (blue). In this diagram, protons and neutrons look like little balls stuck together, but an actual nucleus (as understood by modern nuclear physics) cannot be explained like this, but only by using quantum mechanics. In a nucleus which occupies a certain energy level (for example, the ground state), each nucleon has multiple locations at once. The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911 as a result of Ernest Rutherford's interpretation of the 1909 Geiger–Marsden gold foil experiment performed by Hans Geiger and Ernest Marsden under Rutherford's direction. The proton–neutron model of nucleus was proposed by Dmitry Ivanenko in 1932.[1] Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. The diameter of the nucleus is in the range of 1.75 fm (1.75×10−15 m) for hydrogen (the diameter of a single proton)[2][not in citation given] to about 15 fm for the heaviest atoms, such as uranium. These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 23,000 (uranium) to about 145,000 (hydrogen).
- 21. 9 The branch ofphysics concerned with studying and understanding the atomic nucleus, including its composition and the forces which bind it together, is called nuclear physics. Constituents of Atoms The electrons, protons and neutrons which make up an atom have definite charges and masses. If they are modeled as hard spheres with the same density, they would have the relative sizes shown. While that model should not be taken as reality, it gives us a convenient object to which to attach the definite properties of the particles. rges and masses are precisely known, the sizing is just fun and games. Our best information about the proton and neutron indicates that they are constituent particles, made up of three quarks each. They do however seem to have an effective density which is roughly characteristic of all nuclei, and we can attribute to them a radius of about 1.2 x 10-15 meters. The electron is a fundamental particle, classified as a lepton, which is apparently not made out of any constituent particles. Down to scales of a thousand times smaller than the proton radius quoted above, they have no apparent structure. Electron and Positron
- 22. 10 Electron is thelightest subatomic particle. It is negatively charged particle. Its mass is 9.109 × 10−31 kg which is only 1/1,840 the mass of a proton. An electron is therefore considered to be mass less in comparison with proton and neutron and is not included in calculating atomic mass of an atom. The electron was discovered in 1897 by British Physicist J.J. Thomson during his investigations of cathode rays. His discovery of electron which he initially called corpuscles played a vital role in the structure of an atom. Under ordinary conditions, electrons are bound to the positively charged nuclei by the attraction between opposite electric charges. Any atom may have more or fewer electrons than positively charges and thus be negatively or positively charges as a whole; this charged atoms are known as ions. Some of the electrons are occur in a free state and with ions in the form of matter, which we called it plasma. As one of the leptons, the electron is viewed as one of the fundamental particles. It is a fermion of spin 1/2 and therefore constrained by the Pauli exclusion principle, a fact that has key implications for the building up of the periodic table of elements. The electron's antiparticle, the positron, is identical in mass but has a positive charge. If an electron and a positron encounter each other,they will annihilate with the production of two gamma-rays. On the other hand, one of the mechanisms for the interaction of radiation with matter is the pair production of an electron-positron pair. Associated with the electron is a the electron neutrino. Particle Symbol Anti- particle Rest mass MeV/c2 L(e) L(muon) L(tau) Lifetime (seconds) Electron e- e+ 0.511 +1 0 0 Stable Neutrino (Electron) νe νe 0(<7 x 10-6 ) +1 0 0 Stable
- 23. 11 Proton Proton is asubatomic particle with a positive charge. It has a mass of 1.67262 × 10−27 kg which is 1,836 times of the mass of an electron. When the number of proton is equal to the number of electrons orbiting in nucleus we say that the atom is electrically neutral. Along with neutrons, protons make up the nucleus, held together by the strong force. The proton is a baryon and is considered to be composed of two up quarks and one down quark. It has long been considered to be a stable particle, but recent developments of grand unification models have suggested that it might decay with a half-life of about 1032 years. Experiments are underway to see if such decays can be detected. Decay of the proton would violate the conservation of baryon number, and in doing so would be the only known process in nature which does so. When we say that a proton is made up of two up quarks and a down, we mean that its net appearance or net set of quantum numbers match that picture. The nature of quark confinement suggests that the quarks are surrounded by a cloud of gluons, and within the tiny volume of the proton other quark-antiquark pairs can be produced and then annihilated without changing the net external appearance of the proton. Neutron Neutron is subatomic particle. Neutron does not have any charge, that is, it is neutral. Its mass is 1.67493 × 10−27 kg, greater than that of a proton and electron. Neutrons and protons are commonly called nucleons. The neutron was discovered in 1932 by the English physicist James Chadwick.
- 24. 12 Along with protons,neutrons make up the nucleus, held together by the strong force. The neutron is a baryon and is considered to be composed of two down quarks and one up quark. A free neutron will decay with a half-life of about 10.3 minutes but it is stable if combined into a nucleus. The decay of the neutron involves the weak interaction as indicated in the Feynman diagram to the right. This fact is important in models of the early universe. The neutron is about 0.2% more massive than a proton, which translates to an energy difference of 1.29 MeV. The decay of the neutron is associated with a quark transformation in which a down quark is converted to an up by the weak interaction . The average lifetime of 10.3 min/0.693 = 14.9 minutes is surprisingly long for a particle decay that yields 1.29 MeV of energy. You could say that this decay is steeply "downhill" in energy and would be expected to proceed rapidly. It is possible for a proton to be transformed into a neutron, but you have to supply 1.29 MeV of energy to reach the threshold for that transformation. In the very early stages of the big bang when the thermal energy was much greater than 1.29 MeV, we surmise that the transformation between protons and neutrons was proceeding freely in both directions so that there was an essentially equal population of protons and neutrons. 1.3 Summary
- 25. 13 a. The atomis a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. b. Ordinary matter is made up of protons, neutrons, and electrons and is composed of atoms. An atom consists of a tiny nucleus made up of protons and neutrons, on the order of 20,000 times smaller than the size of the atom. c. Elements are represented by a chemical symbol, with the atomic number and mass number sometimes affixed as indicated below. The mass number is the sum of the numbers of neutrons and protons in the nucleus. d. The electrons, protons and neutrons which make up an atom have definite charges and masses. e. Electron is the lightest subatomic particle. It is negatively charged particle. Proton is a subatomic particle with a positive charge. Neutron is subatomic particle. Neutron does not have any charge, that is, it is neutral. 1.4 Exercise Complete the following sentences using the correct complements! 1. A chemical element consists of those atoms with a specific number of protons in the nucleus; this number is called .... 2. The lightest subatomic particle is called .... It is negatively charged particle. 3. The electron was discovered in .... by British Physicist J.J. Thomson during his investigations of cathode rays 4. Proton is a subatomic particle with a ..... 5. The neutron was discovered in 1932 by the English physicist named .... Check your answer with answer key for the exercise above in part 1.6. 1.5 Formatif Test Choose one correct answer! 1. Which one of the following statements is true for all elements? Neutral atoms of the same element contain A. equal numbers of protons and neutrons. B. equal numbers of protons and electrons. C. equal numbers of neutrons and electrons. D. equal numbers of protons, neutrons and electrons. 2. Who was the first to determine the electron's charge?
- 26. 14 A. Franklin B. Coulomb C.Millikan D. Maxwell 3. An electrically neutral atom is an atom which .... A. does not have any protons or electrons B. has more neutrons than the sum of all its protons and electrons C. has a balance of protons and electrons (the same number of each) D. has a balance of neutrons and electrons (the same number of each) 1.6 Answer Key Exercise answer key 1. The atomic number 2. Electron 3. 1897, J.J. Thomson 4. Positive Charge 5. James Chadwick Formative test Answer key 1. B 2. C 3. C 1.7 Student Worksheet Title : Atom Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Studying the literature about atom Competence : Explain the definition of atom, ion and molecul Indicators : tudents can explain the definition of atoms Information : - Assignments : Read and answer the questions below! 1. explain what the atoms , ions , and molecules !
- 27. 15 2. Consider thefollowing picture ! Atomic number and atomic mass number beside the model is ... A. 2 and 4 B. 6 and 4 C. 4 and 2 D. 4 and 6 ( Ebtanas 1993) Procedurs : 1. Read the literatur about atom : 2. Answer the question above. Assessment : Assessment : For question number 1 : if matching with procedure : 20 For question number 2 : if matching with procedure : 80 2. Studying Activity 2 : ELECTRIC CHARGE 2.1 Learning Strategy 1) Use the demonstration learning method or Cooperative learning method In this studying activity, use the demonstration learning method is better because many subject or objects which must have some demonstration to know and understanding. Demonstrating is the process of teaching through examples or experiments. Cooperative learning is one of the most widespread and fruitful areas of theory, research, and practice in education. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills. 2.2 Electric Charge a. Introduction Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. There are two types of electric charges – positive and negative. Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances; negatively charged substances are repelled
- 28. 16 from negative andattracted to positive. An object will be negatively charged if it has an excess of electrons, and will otherwise be positively charged or uncharged. The SI derived unit of electric charge is the coulomb (C), although in electrical engineering it is also common to use the ampere-hour (Ah), and in chemistry it is common to use the elementary charge (e) as a unit. The symbol Q is often used to denote a charge. The study of how charged substances interact is classical electrodynamics, which is accurate insofar as quantum effects can be ignored (wikipedia ). b. Content The Structure of Matter There is a large overlap of the world of static electricity and the everyday world that you experience. Clothes tumble in the dryer and cling together. You walk across the carpeting to exit a room and receive a door knob shock. You pull a wool sweater off at the end of the day and see sparks of electricity. During the dryness of winter, you step out of your car and receive a car door shock as you try to close the door. Sparks of electricity are seen as you pull a wool blanket off the sheets of your bed. You stroke your cat's fur and observe the fur standing up on its end. Bolts of lightning dash across the evening sky during a spring thunderstorm. And most tragic of all, you have a bad hair day. These are all static electricity events - events that can only be explained by an understanding of the physics of electrostatics. Neutral vs. Charged Objects The number of electrons that surround the nucleus will determine whether or not an atom is electrically charged or electrically neutral. The amount of charge on a single proton is equal to the amount of charge possessed by a single electron. A proton and an electron have an equal amount but an opposite type of charge. Thus, if an atom contains equal numbers of protons and electrons, the atom is described as being electrically neutral. On the other hand, if an atom has an unequal number of protons and electrons, then the atom is electrically charged (and in fact, is then referred to as an ion rather than an atom). Any particle, whether an atom, molecule or ion, that contains less electrons than protons is said to be positively charged. Conversely, any particle that contains more electrons than protons is said to be negatively charged.
- 29. 17 Charged versus UnchargedParticles Positively Charged Negatively Charged Uncharged Possesses more protons than electrons Possesses more electrons than protons Equal numbers of protons and electrons Charged Objects as an Imbalance of Protons and Electrons An atom was described as being a small and dense core of positively charged protons and neutral neutrons surrounded by shells of negatively charged electrons. The protons are tightly bound within the nucleus and not removable by ordinary measures. While the electrons are attracted to the protons of the nucleus, the addition of energy to an atom can persuade the electrons to leave an atom. Similarly, electrons within atoms of other materials can be persuaded to leave their own electron shells and become members of the electrons shells of other atoms of different materials. In short, electrons are migrants - constantly on the move and always ready to try out a new atomic environment. The cause and mechanisms by which this movement of electrons occurs will be the subject . For now, it is sufficient to say that objects that are charged contain unequal numbers of protons and electrons. Charged objects have an imbalance of charge - either more negative electrons than positive protons or vice versa. And neutral objects have a balance of charge - equal numbers of protons and electrons. The principle stated earlier for atoms can be applied to objects. Objects with more electrons than protons are charged negatively; objects with fewer electrons than protons are charged positively. Charge Interactions Suppose that you rubbed a balloon with a sample of animal fur such as a wool sweater or even your own hair. The balloon would likely become charged and its charge would exert a strange influence upon other objects in its vicinity. If some small bits of paper were placed upon a table and the balloon were brought near
- 30. 18 and held abovethe paper bits, then the presence of the charged balloon might create a sufficient attraction for the paper bits to raise them off the table. This influence - known as an electric force - occurs even when the charged balloon is held some distance away from the paper bits. The electric force is a non-contact force. Any charged object can exert this force upon other objects - both charged and uncharged objects. One goal of this unit of The Physics Classroom is to understand the nature of the electric force. Opposites attract. And likes repel. These two fundamental principles of charge interactions will be used throughout the unit to explain the vast array of static electricity phenomena. There are two types of electrically charged objects - those that contain more protons than electrons and are said to be positively charged and those that contain less protons than electrons and are said to be negatively charged. These two types of electrical charges - positive and negative - are said to be opposite types of charge. And consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object. Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite charges, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other. Interaction Between Charged and Neutral Objects The interaction between two like-charged objects is repulsive. The interaction between two oppositely charged objects is attractive. What type of interaction is
- 31. 19 observed between acharged object and a neutral object? The answer is quite surprising to many students of physics. Any charged object - whether positively charged or negatively charged - will have an attractive interaction with a neutral object. Positively charged objects and neutral objects attract each other; and negatively charged objects and neutral objects attract each other. This third interaction between charged and neutral objects is often demonstrated by physics teachers or experienced by students in physics lab activities. For instance, if a charged balloon is held above neutral bits of paper, the force of attraction for the paper bits will be strong enough to overwhelm the downward force of gravity and raise the bits of paper off the table. If a charged plastic tube is held above some bits of paper, the tube will exert an attractive influence upon the paper to raise it off the table. And to the bewilderment of many, a charged rubber balloon can be attracted to a wooden cabinet with enough force that it sticks to the cabinet. Any charged object - plastic, rubber, or aluminum - will exert an attractive force upon a neutral object. And in accordance with Newton's law of action-reaction, the neutral object attracts the charged object. Examples of Phenomenon electric charge : Objects which have been rubbed and it pull the small object exist around it is called an electric charged object. 2.3 Summary 1. Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. 2. There are two types of electric charges – positive and negative are said to be opposite types of charge. 3. Electrically charged or electrical neutral is the number of electrons that surround the nucleus will determine whether or not an atom. 4. The interaction between two like-charged objects is repulsive 5. The interaction between two oppositely charged objects is attractive.
- 32. 20 2.4 Exercise Complete thefollowing sentences using the correct complements! 1. The physical property of matter that causes it to experience a force when close to other electrically charged matter is define of ... 2. There are two types of electric charges that are .... and .... 3. Objects which have been rubbed and it pull the small object exist around it is called an electric charged object is the example of .... 4. The interaction between two like-charged objects is .... 5. The interaction between two oppositely charged objects is .... Check your answer with answer key for the exercise above in part 2.6. 2.5 Formative Test Choose the correct answer! 1. The charge on a glass rod that has been rubbed with silk is called positive: A. by arbitrary convention B. so that the proton charge will be positive C. to conform to the conventions adopted for G and m in Newton's law of gravitation D. because like charges repel E. because glass is an insulator 2. A conductor is distinguished from an insulator with the same number of atoms by the number of : A. nearly free atoms B. electrons C. nearly free electrons D. protons E. molecules 3. A positively charged metal sphere A is brought into contact with an uncharged metal sphere B. As a result: A. both spheres are positively charged B. A is positively charged and B is neutral C. A is positively charged and B is negatively charged D. A is neutral and B is positively charged E. A is neutral and B is negatively charged
- 33. 21 4. A smallobject has charge Q. Charge q is removed from it and placed on a second small object. The two objects are placed 1 m apart. For the force that each object exerts on the other to be a maximum, q should be: A. 2Q B. Q C. Q/2 D. Q/4 E. 0 5. Two identical conducting spheres A and B carry equal charge. They are separated by a distance much larger than their diameters. A third identical conducting sphere C is uncharged. Sphere C is _rst touched to A, then to B, and _nally removed. As a result, the electrostatic force between A and B, which was originally F , becomes: A. F/2 B. F/4 C. 3F/8 D. F/16 E. 0 2.6 Answer Key Exercise Answer key 1. Electric Charge 2. Positive and negative 3. Electric Charge 4. Repulsive 5. Attractive Formative test answer key 1. A 2. C 3. A 4. C 5. C 2.7 Student Worksheet Title : Electric Charge
- 34. 22 Lesson : NaturalScience Semester : 2 Location : Classroom Learning Instruction : Studying the literature about electric charge Competence : Understanding the definition of electric charge, the kinds of electric charge and charge interactions Indicators : Students can understand the definition of electric charge, the kinds of electric charge and charge interactions Information : - Assignments : Read question and answer below! 1. Two electrically charged objects shown in the picture below . If the two objects connected by a wire conductor , determine the direction of the flow of electrons that occurs ! 2. . Look at the picture below ! If there is a charged ball hanging on a rope and dalamposisi as shown above . D If the known positive charge then charge A , B and C consequtive is .... Glass rubbed silk fabric will be positively charged . This occurs because the ... Procedure : 1. Find the literature about electric charge! 2. Studying that literature and then answer the above with yourselves. Assessment : For question number 1 : if matching with procedure : 20 For question number 2 : if matching with procedure : 80 3. Studying Activity 3 : COULOMB LAW 3.1 Learning Strategy
- 35. 23 1) Use thedrill learning method Drill learning method is a method that you always repeat what you learn with give you many exercise. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills. 3.2 Coulomb Law a. Introduction The interaction between charged objects is a non-contact force that acts over some distance of separation. Charge, charge and distance. Every electrical interaction involves a force that highlights the importance of these three variables. Whether it is a plastic golf tube attracting paper bits, two like- charged balloons repelling or a charged Styrofoam plate interacting with electrons in a piece of aluminum, there is always two charges and a distance between them as the three critical variables that influence the strength of the interaction. b. Content Coulomb's Law Equation The quantitative expression for the effect of these three variables on electric force is known as Coulomb's law. Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. In equation form, Coulomb's law can be stated as where Q1 represents the quantity of charge on object 1 (in Coulombs), Q2 represents the quantity of charge on object 2 (in Coulombs), and d represents the distance of separation between the two objects (in meters). The symbol k is a proportionality constant known as the Coulomb's law constant. The value of this constant is dependent upon the medium that the charged objects are immersed in. In the case of air, the value is approximately 9.0 x 109 N • m2 / C2 . If the charged objects are present in water, the value of k can be reduced by as much as a factor of 80. It is worthwhile to point out that the units on k are such that when substituted into the equation the units on
- 36. 24 charge (Coulombs) andthe units on distance (meters) will be canceled, leaving a Newton as the unit of force. Calculations Using Coulomb's Law In physics courses, Coulomb's law is often used as a type of algebraic recipe to solve physics word problems. Three such examples are shown here. Example :Suppose that two point charges, each with a charge of +1.00 Coulomb are separated by a distance of 1.00 meter. Determine the magnitude of the electrical force of repulsion between them.This is not the most difficult mathematical problem that could be selected. It certainly was not chosen for its mathematical rigor. The problem-solving strategy utilized here may seem unnecessary given the simplicity of the given values. Nonetheless, the strategy will be used to illustrate its usefulness to any Coulomb's law problem. The first step of the strategy is the identification and listing of known information in variable form. Here we know the charges of the two objects (Q1 and Q2) and the separation distance between them (d). The next step of the strategy involves the listing of the unknown (or desired) information in variable form. In this case, the problem requests information about the force. So Felect is the unknown quantity. The results of the first two steps are shown in the table below. Given: Q1 = 1.00 C Q2 = 1.00 C d = 1.00 m Find: Felect = ??? The next and final step of the strategy involves substituting known values into the Coulomb's law equation and using proper algebraic steps to solve for the unknown information. This step is shown below. Felect = k • Q1 • Q2 / d2
- 37. 25 Felect = (9.0x 109 N•m2 /C2 ) • (1.00 C) • (1.00 C) / (1.00 m)2 Felect = 9.0 x 109 N 3.3 Summary 1. The quantitative expression for the effect of these three variables on electric force is known as Coulomb's law. 2. Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. 3. In equation form, Coulomb's law can be stated as 3.4 Exercise Complete the following sentences using the correct complements! 1. Coulomb’s Law states .... 2. In equation, Coulomb’s Law can be stated as 3. K in Coulomb’s Law equation is .... 4. Q in Coulomb’s Law equation is .... 5. d in Coulomb’s Law equation is .... Check your answer with answer key for the exercise above in part 3.6 3.5 Formative Test 1. The constant ke, which appears in Coulomb's law formula, is equivalent dimensionally to which of the following? A. N⋅m/C B. N/C C. C. N⋅m2/C2
- 38. 26 D. N/C2 2. Coulomb’slaw relates charge and distance between interacting charged bodies, describing the electrical force as being... A. proportional to the sum of the charge. B. inversely proportional to the distance between charges. C. proportional to the product of the charges and inversely proportional to the distance. D. proportional to the product of the charges and inversely proportional to the distance squared. 3. Two point charges are 4 cm apart. They are moved to a new separation of 2 cm. By what factor does the resulting mutual force between them change? A. ½ B. 2 C. ¼ D. 4 4. If the size of the charge value is tripled for both of two point charges maintained at a constant separation, the mutual force between them will be changed by what factor? E. 9.0 F. 3.0 G. 0.33 H. 1/9 4. If the distance between two point charges is tripled, the mutual force between them will be changed by what factor? A. 9.0 B. 3.0 C. 0.33 D. 1/9 a. Answer Key Exercise Answer Key 1. That the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. 2. Coulomb’s Law
- 39. 27 3. the Coulomb'slaw constant 4. Quantity of Charge 5. Distance a separation between two charge Formative Test answer key 1. C 2. D 3. D 4. A 5. D b. Student Worksheet Title : Coulomb’s Law Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Learn the material about coulomb law Competence : Understanding the concepts of coulomb’s law Indicators : Students can explain the concepts of coulomb’s law Information : Assignments : Read and answer the question below! 1. If the two initial charge is at a distance of 12 cm is approximated to a distance of 4 cm , which occurred coulomb force between the two charges is .... Procedure : 1. Find the literature about coulomb’s law! 2. Studying that literature and then answer the above with yourselves. Assessment : If matching with procedure : 100 4. Studying Activity 4 : ELECTRIC FORCE 4.1 Learning Strategy 1) Use the demonstration learning method In this studying activity, use the demonstration learning method is better because many subject or objects which must have some demonstration to know and understanding. Demonstrating is the process of teaching or learning through examples or experiments. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills.
- 40. 28 4.2 Electric Force a.Introduction Previously in last section, the interactions between charged objects of like charge and opposite charge were discussed. At that time, the two fundamental charge interactions were stated: oppositely charged objects attract and like charged objects repel. These mutual interactions resulted in an electric force between the two charged objects. This force is commonly observed in physics lab activities and classroom demonstrations. We will explore these charge interactions in more detail and begin to quantify it. b. Content Charge Interactions are Forces It is possible that you might have watched two balloons repel each other a dozen or more times and never even thought of the balloon interaction as being a force. Or perhaps you have used a plastic golf tube or other object to raise small paper bits off the lab table and never thought of Newton's laws of motion. Perhaps even now you're thinking, "Why should I? That was the Newton's Laws unit and this is the Static Electricity unit." True. However, the physical world that we study does not separate itself into separate topics, as we teachers and students are prone to do. Physics has an amazing way of fitting together in a seamless fashion. The information that you have forgotten about from the Newton's laws unit has a mischievous way of creeping up on you in other units. That forgetfulness (or negligence or mere ignorance) will haunt you as you try to learn new physics. The more physics that you learn (as in really learn), the more that you come to recognize that the pieces of the physics puzzle fit together to form a unified picture of the world of sight, sound, touch and feel. Here we will explore how Newton's laws of motion fit together with the interaction of charged objects. Suppose that you hold a charged plastic golf tube above a handful of paper bits at rest on the table. The presence of the charged tube is likely to polarize a few bits of paper and then begin to exert an upward pull upon them. The attraction between a charged tube and a polarized (yet neutral) paper bit is an electrical force - Felect. Like all the forces studied in The Physics Classroom, the electrical force is a push or pull exerted upon an object as
- 41. 29 a result ofan interaction with another object. The interaction is the result of electrical charges and thus it is called an electrical force. Unlike many forces that we study, the electrical force is a non-contact force - it exists despite the fact that the interacting objects are not in physical contact with each other. The two objects can act over a separation distance and exert an influence upon each other. In this case, the plastic golf tube pulls upward upon the paper bit and a paper bit pulls downward upon the golf tube. In this case, the force is significantly small. If you were holding the golf tube, you would not likely sense the downward pull exerted upon it by the paper bit. On the other hand, the force is often large enough to either balance or even overwhelm the downward pull of gravity (Fgrav) upon the paper bit and cause it to be elevated or even accelerated off the table. Of course the actual result of the force upon the paper bit is related to Newton's laws and a free-body analysis. If at any moment, the electrical force were greater in magnitude than t h e g r a v itational force, the paper bit would be accelerated upward. And if at any moment, the electrical force is equal in magnitude to the gravitational force, the paper bit will be suspended (or levitated) in midair. The paper bit would be said to be at equilibrium. Now consider the case of the rubber balloons hanging by light threads from the ceiling. If each balloon is rubbed in the same manner (with animal fur), they each become negatively charged and exert a repulsive affect upon each other. This charge interaction results in a force upon each balloon that is directed away from the balloon with which it interacts. Once more, we can identify this repulsive affect as an electrical force. This electrical force joins two other forces that act upon the balloon - the tension force and a force of gravity. Since the balloons are at rest, the three forces must balance each other such that the net force is zero.
- 42. 30 Inverse Square Law Sciencein general and Physics in particular are concerned with relationships. Cause and effect is the focus of science. Nature is probed in order to find relationships and mathematical patterns. Scientists modify a set of conditions to see if there is a pattern of behavior in another set of measurable quantities. The goal is to answer the question of how does a change in a set of variables or conditions causally effect an observable outcome? In Physics, this search for cause and effect leads to questions like: How does a force affect the acceleration of an object? How does the mass of an object affect its acceleration? How does the speed of a falling object affect the amount of air resistance that it experiences? How does the distance from a page to a light bulb affect the amount of light that illuminates the paper's surface? How does the frequency of a sound wave affect the speed at which the sound wave moves? How does the distance between two charged objects affect the force of attraction or repulsion that they encounter? This search for cause and effect often leads to conclusive evidence that two variables are causally related (or not causally related). Careful observation and measurement might indicate that a pattern exists in which an increase in one variable always causes another measurable quantity to increase. This type of cause-effect relationship is described as being a direct relationship. Observation might also indicate that an increase in one variable always causes another measurable quantity to decrease. This type of cause-effect relationship is described as being an inverse relationship. Inverse relationships are common in nature. In electrostatics, the electrical force between two charged objects is inversely related to the distance of separation between the two objects. Increasing the separation distance between objects decreases the force of attraction or repulsion between the objects. And decreasing the separation distance between objects increases the force of attraction or repulsion between the objects. Electrical forces are extremely
- 43. 31 sensitive to distance.These observations are commonly made during demonstrations and lab experiments. Consider a charged plastic golf tube being brought near a collection of paper bits at rest upon a table. The electrical interaction is so small at large distances that the golf tube does not seem to exert an influence upon the paper bits. Yet if the tube is brought closer, an attractive interaction is observed and the strength is so significant that the paper bits are lifted off the table. In a similar manner, charged balloons are observed to exert their greatest influence upon other charged objects when the separation distance is reduced. Electrostatic force and distance are inversely related. The pattern between electrostatic force and distance can be further characterized as an inverse square relationship. Careful observations show that the electrostatic force between two point charges varies inversely with the square of the distance of separation between the two charges. That is, the factor by which the electrostatic force is changed is the inverse of the square of the factor by which the separation distance is changed. So if the separation distance is doubled (increased by a factor of 2), then the electrostatic force is decreased by a factor of four (2 raised to the second power). And if the separation distance is tripled (increased by a factor of 3), then the electrostatic force is decreased by a factor of nine (3 raised to the second power). This square effect makes distance of double importance in its impact upon electrostatic force. The inverse square relationship between force and distance is expressed in the Coulomb's law equation for electrostatic force. , Coulomb's law was stated as This equation is often used as a recipe for algebraic problem solving. This type of use of the Coulomb's law equation was the subject of the previous section. The equation shows that the distance squared term is in the denominator of the equation, opposite the force. This illustrates that force is inversely proportional to the square of the distance.
- 44. 32 4.3 Summary 1. Theelectric force is a universal force that exists between any two charged objects. 2. Between any two charged particles, electric force is vastly greater than the gravitational force. Most observable forces such as those exerted by a coiled spring or friction may be traced to electric forces acting between atoms and molecules. 3. Electrical and magnetism are two aspects of a single electromagnetic force. 4. Moving electric charges produce magnetic forces, and moving magnets produce electric forces. These effects help students to understand electric motors and generators. 5. The strength of the force is proportional to the charges, and, as with gravitation, inversely proportional to the square of the distance between them. 4.4 Exercise Complete the following sentences using the correct complements! 1. A universal force that exists between any two charged objects are know as ... 2. Moving electric charges produce ...., and moving magnets produce ..... 3. Explain the picture! Check your answer with answer key for the exercise above in part 4.6 4.5 Formative Test 1. Which of the following is true of electrical forces? A. Electrical forces are produced by electrical charges B. Like charges attract, unlike charges repel C. Electrical forces are weaker than gravitational forces
- 45. 33 D. Positive andnegative charges can combine to produce a third type of charge 2. A repelling force must occur between two charged objects under which conditions? A. charges are of unlike signs B. charges are of like signs C. charges are of equal magnitude D. charges are of unequal magnitude 3. Doug rubs a piece of fur on a hard rubber rod, giving the rod a negative charge. What happens? A. Protons are removed from the rod. B. Electrons are added to the rod. C. The fur is also charged negatively. D. Negative ions added to the fur. 4. A repelling force must occur between two charged objects under which conditions? A. charges are of like signs B. charges are of unlike signs C. charges are of equal magnitude D. charges are of unequal magnitude 5. An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be: A. Negative. B. Attracted C. Positive D. Repulsed 4.6 Answer Key Exercise answer key 1. Electric Force 2. Magnetic forces, electric force 3. Charges that are same (or like) repel each other. Charges that are different (or unlike) attract each other.
- 46. 34 Formative test answerkey 1. A 2. B 3. B 4. A 5. C 4.7 Student Worksheet Title : Electric Force Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Studying the material about electric force Competence : Understand the concepts of electric force Indicators : Students can understand about the concept of electric force Information : Assignments : Read and answer the questions below! 1. Two electrically charged objects are not similar , the attraction force of F. If the distance of the two charges be kept to 4 times the original , then the force of attraction between the two charges be ... F 2. Two cargo respectively q and 2q is at a distance r experienced by electrostatic force F. If the charge into each plus a charge of second charge q and the distance made half time , the second electrostatic force charge now is ..... Procedure : 1. Find the literature about electric force! 2. Studying that literature and then answer the above with yourselves. Assessment : For question number 1 : if matching with procedure : 20 For question number 2 : if matching with procedure : 80 5 Studying Activity 5 : ELECTRIC FIELD 5.1 Learning Strategy 1) Use the demonstration learning method In this studying activity, use the demonstration learning method is better because many subject or objects which must have some demonstration to know and understanding. Demonstrating is the process of teaching through examples or experiments. 2) Use inquiry approach.
- 47. 35 The inquiry approachis more focused on using and learning content as a means to develop information-processing and problem-solving skills. 5.2 Electric Field a. Introduction Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge. b. Content Action at a Distance How can an object be charged and what affect does that charge have upon other objects in its vicinity? Early in Lesson, we investigated charge interactions - the affect of a charged object upon other objects of the same type of charge, of an opposite type of charge and of no charge whatsoever. In unit 3, the concept of the interaction between charges was revisited and Coulomb's law was introduced to express charge interactions in quantitative terms. In unit 4, electric force was described as a non-contact force. A charged balloon can have an attractive affect upon an oppositely charged balloon even when they are not in contact. The electric force acts over the distance separating the two objects. Electric force is an action-at-a-distance force. In unit 5 of this unit, we will explore this concept of action-at-a-distance using a different concept known as the electric field. As is the usual case, we will begin conceptually and then enter into mathematical expressions that express the concept of an electric field in mathematical terms. The Electric Field Concept As children grow, they become very accustomed to contact forces; but an action-at-a-distance force upon first observation is quite surprising. Seeing two charged balloons repel from a distance or two magnets attract from a distance raises the eyebrow of a child and maybe even causes a chuckle or a "wow." Indeed, an action-at-a-distance or non-contact force is quite unusual. Football players don't run down the field and encounter collision forces from
- 48. 36 five yards apart.The rear-end collision at a stop sign is not characterized by repulsive forces that act upon the colliding cars at a spatial separation of 10 meters. And (with the exception modern WWF wrestling matches) the fist of one fighter does not act from 12 inches away to cause the forehead of a second fighter to be knocked backwards. Contact forces are quite usual and customary to us. Explaining a contact force that we all feel and experience on a daily basis is not difficult. Non-contact forces require a more difficult explanation. After all, how can one balloon reach across space and pull a second balloon towards it or push it away? The best explanation to this question involves the introduction of the concept of electric field. Action-at-a-distance forces are sometimes referred to as field forces. The concept of a field force is utilized by scientists to explain this rather unusual force phenomenon that occurs in the absence of physical contact. While all masses attract when held some distance apart, charges can either repel or attract when held some distance apart. An alternative to describing this action-at-a-distance affect is to simply suggest that there is something rather strange about the space surrounding a charged object. Any other charged object that is in that space feels the affect of the charge. A charged object creates an electric field - an alteration of the space in the region that surrounds it. Other charges in that field would feel the unusual alteration of the space. Whether a charged object enters that space or not, the electric field exists. Space is altered by the presence of a charged object. Other objects in that space experience the strange and mysterious qualities of the space. The strangeness of the space surrounding a charged object is often experienced first hand by the use of a Van de Graaff generator. A Van de Graaff generator is a large conducting sphere that acquires a charge as electrons are scuffed off of a rotating belt as it moves past sharp elongated prongs inside the sphere. The buildup of static charge on the Van de Graaff generator is much greater than that on a balloon rubbed with animal fur or an aluminum plate charged by induction. On a dry day, the buildup of charge becomes so
- 49. 37 great that itcan exert influences on charged balloons held some distance away. If you were to walk near a Van de Graaff generator and hold out your hand, you might even notice the hairs on your hand standing up. And if you were to slowly walk near a Van de Graaff generator, your eyebrows might begin to feel quite staticy. The Van de Graaff generator, like any charged object, alters the space surrounding it. Other charged objects entering the space feel the strangeness of that space. Electric forces are exerted upon those charged objects when they enter that space. The Van de Graaff generator is said to create an electric field in the space surrounding it. Electric Field Intensity The concept of an electric field was introduced. It was stated that the electric field concept arose in an effort to explain action-at-a-distance forces. All charged objects create an electric field that extends outward into the space that surrounds it. The charge alters that space, causing any other charged object that enters the space to be affected by this field. The strength of the electric field is dependent upon how charged the object creating the field is and upon the distance of separation from the charged object. In this section of Lesson 4, we will investigate electric field from a numerical viewpoint - the electric field strength. The Force per Charge Ratio Electric field strength is a vector quantity; it has both magnitude and direction. The magnitude of the electric field strength is defined in terms of how it is measured. Let's suppose that an electric charge can be denoted by the symbol Q. This electric charge creates an electric field; since Q is the source of the electric field, we will refer to it as the source charge. The strength of the source charge's electric field could be measured by any other charge placed somewhere in its surroundings. The charge that is used to measure the electric
- 50. 38 field strength isreferred to as a test charge since it is used to test the field strength. The test charge has a quantity of charge denoted by the symbol q. When placed within the electric field, the test charge will experience an electric force - either attractive or repulsive. As is usually the case, this force will be denoted by the symbol F. The magnitude of the electric field is simply defined as the force per charge on the test charge. If the electric field strength is denoted by the symbol E, then the equation can be rewritten in symbolic form as . The standard metric units on electric field strength arise from its definition. Since electric field is defined as a force per charge, its units would be force units divided by charge units. In this case, the standard metric units are Newton/Coulomb or N/C. In the above discussion, you will note that two charges are mentioned - the source charge and the test charge. Two charges would always be necessary to encounter a force. In the electric world, it takes two to attract or repel. The equation for electric field strength (E) has one of the two charge quantities listed in it. Since there are two charges involved, a student will have to be ultimately careful to use the correct charge quantity when computing the electric field strength. The symbol q in the equation is the quantity of charge on the test charge (not the source charge). Recall that the electric field strength is defined in terms of how it is measured or tested; thus, the test charge finds its way into the equation. Electric field is the force per quantity of charge on the test charge. The electric field strength is not dependent upon the quantity of charge on the test charge. If you think about that statement for a little while, you might be bothered by it. (Of course if you don't think at all - ever - nothing really bothers you. Ignorance is bliss.) After all, the quantity of charge on the
- 51. 39 test charge (q)is in the equation for electric field. So how could electric field strength not be dependent upon q if q is in the equation? Good question. But if you think about it a little while longer, you will be able to answer your own question. (Ignorance might be bliss. But with a little extra thinking you might achieve insight, a state much better than bliss.) Increasing the quantity of charge on the test charge - say, by a factor of 2 - would increase the denominator of the equation by a factor of 2. But according to Coulomb's law, more charge also means more electric force (F). In fact, a twofold increase in q would be accompanied by a twofold increase in F. So as the denominator in the equation increases by a factor of two (or three or four), the numerator increases by the same factor. These two changes offset each other such that one can safely say that the electric field strength is not dependent upon the quantity of charge on the test charge. So regardless of what test charge is used, the electric field strength at any given location around the source charge Q will be measured to be the same. Electric Field Lines The vector nature of the electric field strength was discussed. The magnitude or strength of an electric field in the space surrounding a source charge is related directly to the quantity of charge on the source charge and inversely to the distance from the source charge. The direction of the electric field is always directed in the direction that a positive test charge would be pushed or pulled if placed in the space surrounding the source charge. Since electric field is a vector quantity, it can be represented by a vector arrow. For any given location, the arrows point in the direction of the electric field and their length is proportional to the strength of the electric field at that location. Such vector arrows are shown in the diagram below. Note that the lengths of the arrows are longer when closer to the source charge and shorter when further from the source charge.
- 52. 40 A more usefulmeans of visually representing the vector nature of an electric field is through the use of electric field lines of force. Rather than draw countless vector arrows in the space surrounding a source charge, it is perhaps more useful to draw a pattern of several lines that extend between infinity and the source charge. These pattern of lines, sometimes referred to as electric field lines, point in the direction that a positive test charge would accelerate if placed upon the line. As such, the lines are directed away from positively charged source charges and toward negatively charged source charges. To communicate information about the direction of the field, each line must include an arrowhead that points in the appropriate direction. An electric field line pattern could include an infinite number of lines. Because drawing such large quantities of lines tends to decrease the readability of the patterns, the number of lines is usually limited. The presence of a few lines around a charge is typically sufficient to convey the nature of the electric field in the space surrounding the lines. Electric Field Lines for Configurations of Two or More Charges In the examples above, we've seen electric field lines for the space surrounding single point charges. But what if a region of space contains more than one point charge? How can the electric field in the space surrounding a configuration of two or more charges be described by electric field lines? To answer this question, we will first return to our original method of drawing electric field vectors.
- 53. 41 Suppose that thereare two positive charges - charge A (QA) and charge B (QB) - in a given region of space. Each charge creates its own electric field. At any given location surrounding the charges, the strength of the electric field can be calculated using the expression kQ/d2 . Since there are two charges, the kQ/d2 calculation would have to be performed twice at each location - once with kQA/dA 2 and once with kQB/dB 2 (dA is the distance from that location to the center of charge A and dB is the distance from that location to the center of charge B). The results of these calculations are illustrated in the diagram below with electric field vectors (EA and EB) drawn at a variety of locations. The strength of the field is represented by the length of the arrow and the direction of the field is represented by the direction of the arrow. Since electric field is a vector, the usual operations that apply to vectors can be applied to electric field. That is, they can be added in head-to-tail fashion to determine the resultant or net electric field vector at each location. This is shown in the diagram below. The diagram above shows that the magnitude and direction of the electric field at each location is simply the vector sum of the electric field vectors for each individual charge. If more locations are selected and the process of drawing EA, EB and Enet is repeated, then the electric field strength and direction at a multitude of locations will be known. (This is not done
- 54. 42 since it isa highly time intensive task.) Ultimately, the electric field lines surrounding the configuration of our two charges would begin to emerge. For the limited number of points selected in this location, the beginnings of the electric field line pattern can be seen. This is depicted in the diagram below. Note that for each location, the electric field vectors point tangent to the direction of the electric field lines at any given point. The construction of electric field lines in this manner is a tedious and cumbersome task. The use of a field plotting computer software program or a lab procedure produces similar results in less time (and with more phun). Whatever the method used to determine the electric field line patterns for a configuration of charges, the general idea is that the pattern is the resultant of the patterns for the individual charges within the configuration. The electric field line patterns for other charge configurations are shown in the diagrams below. After plotting the electric field line patterns for a variety of charge configurations, the general patterns for other configurations can be predicted. There are a number of principles that will assist in such predictions. These principles are described (or re-described) in the list below. Electric field lines always extend from a positively charged object to a negatively charged object, from a positively charged object to infinity, or from infinity to a negatively charged object.
- 55. 43 Electric fieldlines never cross each other. Electric field lines are most dense around objects with the greatest amount of charge. At locations where electric field lines meet the surface of an object, the lines are perpendicular to the surface. 5.3 Summary 1. Electric field is defined as the electric force per unit charge. 2. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. 3. An electric field is a vector field that permeates the space around electrical charge.It is what mediates the force between that charge and any other charge nearby. It is also caused (induced) by a changing magnetic field. 4. Electric field is a vector with units of newtons per coulomb (N/C) or volts per metre (V/m), and dimensions of mass.length/charge.time² (ML/QT²). 5.4 Exercise Complete the following sentences using the correct complements! 1. The electric force per unit charge is defined of .... 2. Units of electric field is .... 3. Dimensions of electric field is.... Check your answer with answer key for the exercise above in part 5.6 5.5 Formative Test 1. An electric field is most directly related to: A. the momentum of a test charge B. the kinetic energy of a test charge C. the potential energy of a test charge D. the force acting on a test charge E. the charge carried by a test charge 2. Experimenter A uses a test charge q0 and experimenter B uses a test charge 2q0 to measure an electric field produced by stationary charges. A finds a field that is: A. the same in both magnitude and direction as the field found by B
- 56. 44 B. greater inmagnitude than the field found by B C. less in magnitude than the field found by B D. opposite in direction to the field found by B E. either greater or less than the field found by B, depending on the accelerations of the test charges 3. Two thin spherical shells, one with radius R and the other with radius 2R, surround an isolated charged point particle. The ratio of the number of field lines through the larger sphere to the number through the smaller is: A. 1 B. 2 C. 4 D. ½ E. 1/4 4. An electron traveling north enters a region where the electric field is uniform and points north. The electron: A. speeds up B. slows down C. veers east D. veers west E. continues with the same speed in the same direction 5. An electric field exerts a torque on a dipole only if: A. the field is parallel to the dipole moment B. the field is not parallel to the dipole moment C. the field is perpendicular to the dipole moment D. the field is not perpendicular to the dipole moment E. the field is uniform 5.6 Answer Key Exercise answer key 1. Electric field 2. N/C) or volts per metre (V/m), 3. (ML/QT²). Formative test answer key 1. D 2. A
- 57. 45 3. A 4. B 5.B 5.7 Student Worksheet Title : Electric Field Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Studying the material about electric Field! Competence : Understanding the concept of electric field Indicators : Students can explain the concept of electric field Information : Assignments : Read and answer the questions below! 1. Electric field strength at a point in an electric field F is 4.5 x 104 N / C to the direction toward the charge . If the point was within 1 meter of the cargo M , determine the amount and type of electrical charge M ! Procedure : 1. Find the literature about electric field! 2. Studying that literature and then answer the above with yourselves. Assessment : If macthing with the procedure, the value 100. 6 Studying Activity 6 : ELECTRIC FLUX 6.1 Learning Strategy 1) Use the Collaboration learning method Collaboration allows students to actively participate in the learning process by talking with each other and listening to other points of view. Collaboration establishes a personal connection between students and the topic of study and it helps students think in a less personally biased way. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills. 6.2 Electric Flux a. Introduction A measure of the strength of an electric field generated by a free electric charge, corresponding to the number of electric lines of force passing through a given area. It is equal to the electric field strength multiplied by the
- 58. 46 permittivity of thematerial through which the electric field extends. It is measured in coulombs per square meter. Also called electric displacement. b. Content Electric flux, property of an electric field that may be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. Electric field lines are considered to originate on positive electric charges and to terminate on negative charges. Field lines directed into a closed surface are considered negative; those directed out of a closed surface are positive. If there is no net charge within a closed surface, every field line directed into the surface continues through erior and is directed outward elsewhere on the surface. The concept of electric flux is useful in association with Gauss' law. The electric flux through a planar area is defined as the electric field times the component of the area perpendicular to the field. If the area is not planar, then the evaluation of the flux generally requires an area integral since the angle will be continually changing.
- 59. 47 When the areaA is used in a vector operation like this, it is understood that the magnitude of the vector is equal to the area and the direction of the vector is perpendicular to the area. In electromagnetism, electric flux is the rate of flow of the electric field through a given area. Electric flux is proportional to the number of electric field lines going through a virtual surface. If the electric field is uniform, the electric flux passing through a surface of vector area S is where E is the electric field (having units of V/m), E is its magnitude, S is the area of the surface, and θ is the angle between the electric field lines and the normal (perpendicular) to S. For a non-uniform electric field, the electric flux dΦE through a small surface area dS is given by (the electric field, E, multiplied by the component of area perpendicular to the field). The electric flux over a surface S is therefore given by the surface integral: where E is the electric field and dS is a differential area on the closed surface S with an outward facing surface normal defining its direction. For a closed Gaussian surface, electric flux is given by: where E is the electric field,
- 60. 48 S is anyclosed surface, Q is the total electric charge inside the surface S, ε0 is the electric constant (a universal constant, also called the "permittivity of free space") (ε0 ≈ 8.854 187 817... x 10−12 farads per meter (F·m−1 )). This relation is known as Gauss' law for electric field in its integral form and it is one of the four Maxwell's equations. It is important to note that while the electric flux is not affected by charges that are not within the closed surface, the net electric field, E, in the Gauss' Law equation, can be affected by charges that lie outside the closed surface. While Gauss' Law holds for all situations, it is only useful for "by hand" calculations when high degrees of symmetry exist in the electric field. Examples include spherical and cylindrical symmetry. Electrical flux has SI units of volt metres (V m), or, equivalently, newton metres squared per coulomb (N m2 C−1 ). Thus, the SI base units of electric flux are kg·m3 ·s−3 ·A−1 . Its dimensional formula is [L3 MT–1 I–1 ]. 6.3 Summary 1. The electric flux through an area is defined as the electric field multiplied by the area of the surface projected in a plane perpendicular to the field. 2. The concept of electric flux is useful in association with Gauss' law. 3. The electric flux through a planar area is defined as the electric field times the component of the area perpendicular to the field. 6.4 Exercise 1. Electeric flux are defined .... 2. The equation of electric flux is .... 3. Electric flux SI units is .... 4. The dimensional formula for electric flux is .... 5. This relation is known as .... for electric field in its integral form and it is one of the four Maxwell's equations 6.5 Formative Test
- 61. 49 1. Two smallconducting spheres attract one another electrostatically. This can occur for a variety of reasons. Which of the following statements MUST be true? B. At least one sphere is charged. C. Neither sphere is charged. D. Both are charged. E. Both have the same sign of charge. 2. A cubical surface with sides 2.0 m long is oriented with its right and left faces perpendicular to a uniform electric field ~E = 1.6 × 105 ˆı N/C. The net charge enclosed by this surface is approximately A. 8.0 × 104 ε0. B. 3.2 × 105 ε0. C. 6.4 × 105 ε0. D. 0. 3. A surface is constructed so that at all points on the surface the electric field, ~E, points inward. It can be concluded that A. the surface encloses a net positive charge. B. the surface encloses a net negative charge. C. the infinitesimal surface vector, d~A at all points on the surface is necessarily parallel to the electric field vector, ~E. D. the infinitesimal surface vector, d~A at all points on the surface is necessarily perpendicular to the electric field vector, ~E. 4. A solid, conducting sphere of radius R is positively charged. Of the following distances from the center of the sphere, which location will have the greatest electric potential? (Take V=0 at r ! 1) A. 0 (center of the sphere). B. 1.1 R. C. 1.25 R. D. None of the above because the potential is constant. 5. A very long wire contains a uniform negative charge density −λ. A charge −q rests inside a spherical
- 62. 50 Gaussian surface ofradius R. The sphere’s center lies on the wire. Located outside the sphere is another charge +q. What is the total electric flux through the sphere? 6.6 Answer Key Exercise answer key 1. as the electric field multiplied by the area of the surface projected in a plane perpendicular to the field 2. 3. volt metres (V m), or, equivalently, newton metres squared per coulomb (N m2 C−1 ). Thus, the SI base units of electric flux are kg·m3 ·s−3 ·A−1 . 4. Its dimensional formula is [L3 MT–1 I–1 ]. 5. Gauss’s Law Formative answer key 1. A 2. D 3. B 4. A 5. D 6.7 Student Worksheet Title : Electric Flux Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Learn the material about electric flux Competence : Understanding the concept of electric flux Indicators : Students can using the concept of electric for answer the problem. Information : Assignments : Read and answer the question below! A field of 500 cm2 exposed to strong homogeneous electric field with the angle of arrival
- 63. 51 by 45 °. If large field strength of 200 N / C , electric field flux that occurs in the area by .... Procedure : 1. Find the literature about electric force! 2. Studying that literature and then answer the above with yourselves. Assessment : If matching with procedure : 100 7 Studying Activity 7 : ELECTRIC POTENTIAL 7.1 Learning Strategy 1) Use the Collaboration learning method Collaboration allows students to actively participate in the learning process by talking with each other and listening to other points of view. Collaboration establishes a personal connection between students and the topic of study and it helps students think in a less personally biased way. 2) Use inquiry approach. The inquiry approach is more focused on using and learning content as a means to develop information-processing and problem-solving skills. 7.2 Electric Potential a. Introduction A gravitational analogy was relied upon to explain the reasoning behind the relationship between location and potential energy. Moving a positive test charge against the direction of an electric field is like moving a mass upward within Earth's gravitational field. Both movements would be like going against nature and would require work by an external force. This work would in turn increase the potential energy of the object. On the other hand, the movement of a positive test charge in the direction of an electric field would be like a mass falling downward within Earth's gravitational field. Both movements would be like going with nature and would occur without the need of work by an external force. This motion would result in the loss of potential energy. Potential energy is the stored energy of position of an object and it is related to the location of the object within a field. In this section of Lesson 1, we will introduce the concept of electric potential and relate this concept to the potential energy of a positive test charge at various locations within an electric field.
- 64. 52 b. Content A gravitationalfield exists about the Earth that exerts gravitational influences upon all masses located in the space surrounding it. Moving an object upward against the gravitational field increases its gravitational potential energy. An object moving downward within the gravitational field would lose gravitational potential energy. it was defined as the energy stored in an object due to its vertical position above the Earth. The amount of gravitational potential energy stored in an object depended upon the amount of mass the object possessed and the amount of height to which it was raised. Gravitational potential energy depended upon object mass and object height. An object with twice the mass would have twice the potential energy and an object with twice the height would have twice the potential energy. It is common to refer to high positions as high potential energy locations. A glance at the diagram at the right reveals the fallacy of such a statement. Observe that the 1 kg mass held at a height of 2 meters has the same potential energy as a 2 kg mass held at a height of 1 meter. Potential energy depends upon more than just location; it also depends upon mass. In this sense, gravitational potential energy depends upon at least two types of quantities: 1) Mass - a property of the object experiencing the gravitational field, and 2) Height - the location within the gravitational field So it is improper to refer to high positions within Earth's gravitational field as high potential energy positions. But is there a quantity that could be used to rate such heights as having great potential of providing large quantities of potential energy to masses that are located there? Yes! While not discussed during the unit on gravitational potential energy, it would have been possible to introduce a quantity known as gravitational potential - the potential energy per kilogram. Gravitational potential would be a quantity that could be used to rate various locations about the surface of the Earth in terms of how much potential energy each kilogram of mass would possess when placed there. The quantity of gravitational potential is defined as the PE/mass. Since both
- 65. 53 the numerator andthe denominator of PE/mass are proportional to the object's mass, the expression becomes mass independent. Gravitational potential is a location-dependent quantity that is independent of the mass of the object experiencing the field. Gravitational potential describes the affects of a gravitational field upon objects that are placed at various locations within it. If gravitational potential is a means of rating various locations within a gravitational field in terms of the amount of potential energy per unit of mass, then the concept of electric potential must have a similar meaning. Consider the electric field created by a positively charged Van de Graaff generator. The direction of the electric field is in the direction that a positive test charge would be pushed; in this case, the direction is outward away from the Van de Graaff sphere. Work would be required to move a positive test charge towards the sphere against the electric field. The amount of force involved in doing the work is dependent upon the amount of charge being moved (according to Coulomb's law of electric force). The greater the charge on the test charge, the greater the repulsive force and the more work that would have to be done on it to move it the same distance. If two objects of different charge - with one being twice the charge of the other - are moved the same distance into the electric field, then the object with twice the charge would require twice the force and thus twice the amount of work. This work would change the potential energy by an amount that is equal to the amount of work done. Thus, the electric potential energy is dependent upon the amount of charge on the object experiencing the field and upon the location within the field. Just like gravitational potential energy, electric potential energy is dependent upon at least two types of quantities: 1) Electric charge - a property of the object experiencing the electrical field, and 2) Distance from source - the location within the electric field While electric potential energy has a dependency upon the charge of the object experiencing the electric field, electric potential is purely location dependent. Electric potential is the potential energy per charge. The concept of electric potential is used to express the affect of an electric field of a
- 66. 54 source in termsof the location within the electric field. A test charge with twice the quantity of charge would possess twice the potential energy at a given location; yet its electric potential at that location would be the same as any other test charge. A positive test charge would be at a high electric potential when held close to a positive source charge and at a lower electric potential when held further away Because an electric field exerts a force on any charge in that field, and because that force causes charges to move a certain distance, we can say that an electric field does work on charges. Consequently, we can say that a charge in an electric field has a certain amount of potential energy, U. Just as we saw in the chapter on work, energy, and power, the potential energy of a charge decreases as work is done on it: WORK 1. When the charge moves a distance r parallel to the electric field lines, the work done is qEr. 2. When the charge moves a distance r perpendicular to the electric field lines, no work is done. 3. When the charge moves a distance r at an angle to the electric field lines, the work done is qEr cos . 7.3 Summary 1. Gravitational potential energy depends upon at least two types of quantities: Mass - a property of the object experiencing the gravitational field, and Height - the location within the gravitational field. 2. Electric potential energy is dependent upon at least two types of quantities: Electric charge - a property of the object experiencing the electrical field, and Distance from source - the location within the electric field 7.4 Exercise 1. The unit of electrical potential is ....
- 67. 55 2. Gravitational potentialenergy depends upon at least two types of quantities that is .... 3. Electric potential energy is dependent upon at least two types of quantities .... 7.5 Formative Test 1. The unit of electrical potential, the volt, is dimensionally equivalent to: A. J⋅C. B. J/C C. C/J D. J 2. The quantity of electrical potential, the volt, is dimensionally equivalent to: A. force/charge. B. force × charge. C. electric field × distance. D. electric field/distance 3. A free electron is in an electric field. With respect to the field, it experiences a force acting: A. parallel. B. anti-parallel (opposite in direction). C. perpendicular. D. along a constant potential line. 4. If the distance between two negative point charges is increased by a factor of three, the resultant potential energy is what factor times the initial potential energy? A. 3.0 B. 9.0 C. 1/3 D. 1/9
- 68. 56 5. An electronin a TV picture tube is accelerated through a potential difference of 10 kV before it hits the screen. What is the kinetic energy of the electron in electron volts? (1 eV = 1.6 × 10−19 J) A. 1.0 × 104 eV B. 1.6 × 10−15 eV C. 1.6 × 10−22 eV D. 6.25 × 1022 eV 7.6 Answer Key Exercise answer key 1. J/C 2. Mass and Height 3. Electric charge and Distance from source Formative test answer key 1. B 2. C 3. B 4. C 5. A 7.7 Student Worksheet Title : Electric Potential Lesson : Natural Science Semester : 2 Location : Classroom Learning Instruction : Learn the material about electric potential Competence : Understanding the concept of electric potential Indicators : Students can using the concept of electric potential for some problem Information : Assignments : Read and answer the questions below Point A and point B has an electric potential difference of 12 volts . Determine the energy needed to bring 6μ Coulomb electric charge from one point A to point B ! Procedure : 1. Find the literature about electric potential! 2. Studying that literature and then answer the above with yourselves. Assessment : If matching with procedure : 100
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- 70. 56 EVALUATION Kognitif Skill QUESTIONS Questions : 1.What is atom ? 2. What is the relationship of atoms and electric charge? 3. Which particles have charges? 4. ____ are the charged parts of an atom. a. Only electrons b. Only protons c. Electrons and neutrons d. Electrons and protons e. Protons and neutrons 5. What is electron, proton, and neutron? 6. On two occasions, the following charge interactions between balloons A, B and C are observed. In each case, it is known that balloon B is charged negatively. Based on these observations, what can you conclusively confirm about the charge on balloon A and C for each situation. 7. What does the electric field look like? 8. What does the electrical force do? 9. The Q in Coulomb's law equation stands for the _____. a. mass of a charged object b. of excess electrons on the object c. the current of a charged object d. the distance between charged objects e. charge of a charged object 10. The quantity electric potential is defined as the amount of _____. a. Electric potential energy b. Force acting upon a charge c. potential energy per charge d. force per charge
- 71. 57 11. When aplastic rod is charged negatively by friction, a. it gains electrons only b. it gains more electrons than protons c. it loses protons only d. it loses more protons than electrons 12. M, N, O, and P are pith balls which behaves as follows; M repels N; M attracts O; O repels P. If P is positively charged, a. N must be positively charged b. N must be negatively charged c. N must be positively charge or neutral d. N must be negatively charged or neutral 13. What will happen if a positive charge of static electricity is placed in an electric field? a. A force is produced on the charge. b. The charge will become negative. c. The charge will remain positive but become smaller. d. The charge will remain positive but become larger. 14. A positively charge pith ball attracts another suspended pith ball. Which of the following statements about the second pith ball is correct? a. It must have fewer positive charges b. It does not need to be charge c. It must be negatively charged d. It must be earthed 15. An ebonite rod is rubbed with fur and the rod becomes negatively charged because: . . . . a. the fur has some electrons to the rod b. the rod has gained some electrons from the fur c. the fur has gained some proton the rod d. the rod has gained some protons to the fur 16. Why is a positively charged object made neutral (discharged) by someone touching it? a. Protons flow from the object b. Electrons flow from the object c. Protons flow onto the object d. Electrons flow onto the object 17. An electrically “earthed” or “ grounded” object is . . . . a. Buried underground b. Insulated from other electrical devices c. Connected to zero potential d. Touching the floor thrught an insulator 18. The two uncharged metal spheres, R and S shown in the figure below are separated while the negatively charged polythene strips is held near R. The resulting charges on R and S are : . . . R S A. positive positive B. negative negative C. negative positive D. positive negative R S
- 72. 58 19. Consider thefigure below! If A and B connected with conductor, so . . . . . a. VA > VB so the electrons flow from A to B 3 electrons. b. VA < VB so the electrons flow from A to B 3 electrons c. VA > VB so the electrons flow from B to A 6 electrons d. VA < VB so the electrons flow from B to A 6 electrons 20. Two objects with electrical charged each of them +2,5 coulomb and -4 coulomb separated between distance 2 cm. How much is the force between the two objects? a. 4,5 x 1012 N b. 4,5 x 1011 N c. 2,25 x 1014 N d. 225 x 1014 N A B
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