This document discusses various topics in electrostatics including:
1) Electric charge can be positive or negative and like charges repel while unlike charges attract.
2) Charge is conserved meaning the total amount of charge in a system remains constant during interactions and transformations.
3) The coulomb is the SI unit for electric charge and small amounts are measured in microcoulombs. The elementary charge is the smallest unit of charge possible.
4) Materials can be conductors, insulators or semiconductors depending on how freely charge can flow through them.
1. Static electricity is caused by the transfer of electrons between two objects during friction, such as hair becoming charged after rubbing against a sweater.
2. When a duster is rubbed against polythene, electrons transfer from the duster to the polythene, leaving the duster positively charged and the polythene negatively charged.
3. Insulators like silk and polythene remain charged after friction because electrons cannot move within them, while conductors like copper allow electrons to move freely and are charged through induction.
Electricity and Magnetism is a lesson introducing students to concepts like static electricity, electric circuits, electromagnetism, and more. It defines key terms like electricity, static electricity, voltage, current, conductors and insulators. Students learn that rubbing objects can cause a transfer of electrons leading to static charges. The relationship between electricity and magnetism is explored through electromagnets, generators, motors and electromagnetic induction. Direct current from batteries is contrasted with alternating current from generators that switches direction periodically.
The document discusses static electricity and electrostatics. It explains that:
- Charged objects can be charged through friction or induction. Friction charging involves the transfer of electrons, while induction charging uses the redistribution of existing electrons in a conductor.
- Like charges repel and unlike charges attract, following Coulomb's law. The direction and strength of electric fields can be represented by field lines.
- Applications include photocopiers, which use photoconductivity and electrostatic attraction/repulsion to transfer toner images to paper. Hazards include lightning and electrostatic discharge damaging electronics.
Static electricity occurs when materials are rubbed together, causing an excess of electric charges on their surfaces. This can result in attraction or repulsion between objects and even sparks. The triboelectric series lists materials based on their tendency to gain or lose electrons when in contact with another material. Sparks require the presence of both conductors and insulators and occur when a large enough potential difference builds up to allow a discharge of electrons across a gap.
1. Charging by friction is demonstrated using a plastic straw and tissue paper. Rubbing the straw with tissue gives it a static charge, causing small bits of paper to be attracted.
2. There are two types of electrical charges: positive and negative. Charge is measured in coulombs. Unlike charges attract and like charges repel according to Coulomb's law.
3. An electric field is a region where an electric charge would experience force. It is represented by electric field lines originating from positive charges and terminating on negative charges.
Static electricity is a stationary electrical charge that builds up on the surface of materials. It occurs when electrons are transferred between objects through friction, contact, or induction, leaving one object with an excess of electrons (negative charge) and the other lacking electrons (positive charge). Insulators do not allow electron flow and can more easily build up static charges, while conductors allow electron flow and cannot. Grounding neutralizes charges by allowing electrons to flow to or from the earth. Lightning is a natural discharge of built-up static electricity in clouds, traveling jaggedly through the air in search of the fastest path to ground. Lightning rods provide this path to protect buildings.
1. Electrostatic forces are caused by the attraction and repulsion of electric charges, such as when objects are rubbed together.
2. Atoms become charged when they gain or lose electrons, forming ions. The structure of the atom is such that electrons orbit a small, dense nucleus at relatively large distances.
3. Charged objects interact through electric fields and can attract or repel one another depending on whether their charges are opposite or the same. Applications of electrostatic forces include photocopiers, spray painting, and identifying atoms through spectroscopy.
1. Static electricity is caused by the transfer of electrons between two objects during friction, such as hair becoming charged after rubbing against a sweater.
2. When a duster is rubbed against polythene, electrons transfer from the duster to the polythene, leaving the duster positively charged and the polythene negatively charged.
3. Insulators like silk and polythene remain charged after friction because electrons cannot move within them, while conductors like copper allow electrons to move freely and are charged through induction.
Electricity and Magnetism is a lesson introducing students to concepts like static electricity, electric circuits, electromagnetism, and more. It defines key terms like electricity, static electricity, voltage, current, conductors and insulators. Students learn that rubbing objects can cause a transfer of electrons leading to static charges. The relationship between electricity and magnetism is explored through electromagnets, generators, motors and electromagnetic induction. Direct current from batteries is contrasted with alternating current from generators that switches direction periodically.
The document discusses static electricity and electrostatics. It explains that:
- Charged objects can be charged through friction or induction. Friction charging involves the transfer of electrons, while induction charging uses the redistribution of existing electrons in a conductor.
- Like charges repel and unlike charges attract, following Coulomb's law. The direction and strength of electric fields can be represented by field lines.
- Applications include photocopiers, which use photoconductivity and electrostatic attraction/repulsion to transfer toner images to paper. Hazards include lightning and electrostatic discharge damaging electronics.
Static electricity occurs when materials are rubbed together, causing an excess of electric charges on their surfaces. This can result in attraction or repulsion between objects and even sparks. The triboelectric series lists materials based on their tendency to gain or lose electrons when in contact with another material. Sparks require the presence of both conductors and insulators and occur when a large enough potential difference builds up to allow a discharge of electrons across a gap.
1. Charging by friction is demonstrated using a plastic straw and tissue paper. Rubbing the straw with tissue gives it a static charge, causing small bits of paper to be attracted.
2. There are two types of electrical charges: positive and negative. Charge is measured in coulombs. Unlike charges attract and like charges repel according to Coulomb's law.
3. An electric field is a region where an electric charge would experience force. It is represented by electric field lines originating from positive charges and terminating on negative charges.
Static electricity is a stationary electrical charge that builds up on the surface of materials. It occurs when electrons are transferred between objects through friction, contact, or induction, leaving one object with an excess of electrons (negative charge) and the other lacking electrons (positive charge). Insulators do not allow electron flow and can more easily build up static charges, while conductors allow electron flow and cannot. Grounding neutralizes charges by allowing electrons to flow to or from the earth. Lightning is a natural discharge of built-up static electricity in clouds, traveling jaggedly through the air in search of the fastest path to ground. Lightning rods provide this path to protect buildings.
1. Electrostatic forces are caused by the attraction and repulsion of electric charges, such as when objects are rubbed together.
2. Atoms become charged when they gain or lose electrons, forming ions. The structure of the atom is such that electrons orbit a small, dense nucleus at relatively large distances.
3. Charged objects interact through electric fields and can attract or repel one another depending on whether their charges are opposite or the same. Applications of electrostatic forces include photocopiers, spray painting, and identifying atoms through spectroscopy.
Interactive textbook ch. 17 introduction to electricitytiffanysci
1) Friction and induction are the two main causes of static electricity.
2) Static electricity builds up in clouds during thunderstorms as water droplets, ice, and air move within the storm cloud, transferring negative charges.
3) Lightning rods help protect buildings by providing a path for the electric charges from lightning to safely move to the ground through the rod's wire connection.
This document discusses charge, lightning, and thunderstorms. It begins by defining electric charge and describing the three types of charges: positive, negative, and neutral. Charge can be transferred between objects through friction, conduction, or induction. Lightning is a large-scale electric spark that occurs during thunderstorms due to the buildup of charges in clouds. Earthing is the process of safely transferring excess charge from an object to the ground. During a thunderstorm, it is important to find shelter inside a building or vehicle and avoid open areas, tall objects, and water sources.
Interactive textbook ch. 18 sec 1 magnets & magnetismtiffanysci
Magnets have two poles, north and south, and exert magnetic forces on each other and other objects. Earth itself acts like a giant magnet, with its magnetic north pole located near its geographic south pole. Materials are magnetic if their atomic domains are aligned, allowing their magnetic fields to combine. There are different types of magnets including permanent and electromagnets. Earth's rotation creates electric currents in its liquid outer core, generating the planet's magnetic field.
Electrostatics is the study of electric charges at rest and the forces between them. Electrical forces act over short distances and opposite charges attract while like charges repel based on Coulomb's law. Materials are classified as conductors or insulators based on how tightly bound their electrons are. Objects can be charged through contact/friction or induction and develop a non-uniform distribution of charge known as polarization. An electric field is created by a charged object and defined as the region in which a test charge would experience force, with field lines indicating direction. Electric potential energy is the energy a charge has based on its position in an electric field. Capacitors can store electric energy by separating opposite charges on conducting plates.
This document discusses static electricity and how objects become electrically charged. It describes three main ways that objects can become charged: 1) charging by friction, where electrons are transferred between two objects in contact with each other; 2) charging by conduction, where charge flows through a conducting material when it touches a charged object; and 3) charging by induction, where a charged object induces a charge in a nearby object without direct contact. The document also discusses properties of charges, insulators and conductors, electroscopes for detecting charge, lightning formation in clouds, and how a Van de Graaff generator works to produce high voltages.
An electroscope is a device used to test if an object is charged. It consists of a metal ball, rod and leaves. When neutral, the leaves stay together, but when charged, they repel each other. Charging can occur through contact or induction. Induction involves charging an object without direct contact by using a nearby charged object to move its electrons. Grounding provides a path for charges to travel to or from the ground.
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge.
Here are some examples of static electricity in our day to day life:
When we walk on a carpeted floor and getting shock when touching a door knob or any other metal object is one of the best examples of static electricity.
Clothes stuck to one another after being in the dryer is another example of static electricity.
Static electricity is caused by an imbalance of electric charges, usually electrons, on the surface of materials. When certain materials are rubbed together, electrons can be transferred, leaving one material with an excess of electrons and a negative charge, and the other with a deficit of electrons and a positive charge. These imbalanced charges attract or repel each other, causing phenomena like balloons sticking to walls or hair standing on end. Lightning is a large-scale example of static electricity, where the bottoms of thunderclouds become negatively charged and the tops positively charged, until a discharge occurs as lightning.
The document summarizes static electricity and different models that were proposed to explain it. It discusses the two-fluid model proposed by Charles Dufay involving vitreous and resinous fluids. It then discusses Benjamin Franklin's one-fluid model involving positive and negative charges. Finally, it introduces the modern particle model involving electrons, protons and neutrons to explain how objects become charged through the gain or loss of electrons.
Electric charge is a fundamental property of matter that causes electromagnetic attraction and repulsion. The electric charge is quantized, meaning it occurs in discrete integer multiples of the elementary charge carried by a single electron or proton. Robert Millikan's oil drop experiment directly demonstrated the quantization of charge by measuring the electric charges on tiny oil droplets, finding they were always integer multiples of approximately 1.6×10^-19 coulombs. Coulomb's law describes the electric force between two charged particles, stating it is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Static electricity occurs when objects become electrically charged through the transfer of electrons. Charging occurs when two materials are rubbed together, causing electrons to move from one material to the other. This leaves one material with an excess of electrons and a negative charge, and the other material with a deficit of electrons and a positive charge. The electric charges remain on the surface of the objects until they are given a path to ground or neutralize each other through contact or discharge.
The document discusses different aspects of electric charge including:
1) Atoms contain protons, neutrons, and electrons. Objects with equal numbers of protons and electrons are neutral, while imbalances lead to electric charges.
2) Charged objects exert electric forces on each other - opposites attract and likes repel. The elementary charge unit is 1 electron or proton.
3) Neutral objects can become polarized when near a charged object, gaining opposite charges on opposite sides and becoming attracted to both positive and negative charges.
Electrons, protons, and neutrons are the main subatomic particles that make up atoms. Electrons have a negative charge and orbit the nucleus, while protons have a positive charge in the nucleus. Neutrons have no charge. Atoms consist of a nucleus surrounded by electrons. When an object gains or loses electrons through friction or contact with another object, it becomes positively or negatively charged respectively, as gaining or losing electrons leaves the object with an excess or deficit of protons. Charging by contact occurs when a charged object transfers charge to a neutral object they touch.
This document provides an overview of electricity and electrical engineering concepts. It discusses the following key points:
- Electricity is a fundamental property of nature that is observed and exploited, though not fully explained. It is a source of energy.
- Atoms are made up of protons, neutrons, and electrons. Protons are positively charged, electrons are negatively charged, and their interactions hold atoms together.
- Electric charge is a phenomenon associated with atomic particles. The fundamental unit of charge is the coulomb. Charged particles experience attractive or repulsive forces depending on whether their charges are opposite or alike.
- Electrons in atoms occupy discrete energy levels or bands. Insulators have a large gap between
Static electricity occurs when there is a build up of electric charge on the surface of a material without the flow of electric current. It results from the transfer of electrons between two materials during friction like rubbing a balloon on hair. This can cause attraction between materials with opposite charges like a negatively charged balloon and positively charged hair. Common examples are rubbing a plastic ruler to attract paper or walking on carpet and touching a doorknob to discharge. Different materials have different tendencies to gain or lose electrons through friction based on their electron affinity.
This document provides an overview of forces and motion. It discusses the four fundamental forces - strong nuclear, weak nuclear, electromagnetic, and gravitational. It explains how static electricity is caused by an imbalance of electrons on objects. Experiments are described to demonstrate the attraction and repulsion of charged objects. The document also covers electromagnetism, generators, motors, gravity, and Newton's laws of motion. Key concepts include like charges repelling and opposite charges attracting, and that in a vacuum all objects fall at the same rate regardless of mass.
A positive charge occurs when an object has fewer electrons than protons, giving it an excess of protons. This excess of protons causes a negative charge to accumulate on nearby objects, resulting in an attractive electrostatic force. Positive charges are used to generate electric currents and in applications like spray painting. A negative charge is an excess of electrons, causing the object to attract other positively charged particles. Neutral objects have an equal number of protons and electrons, resulting in no net electric charge.
This document provides an overview of basic electricity concepts including:
- Conductors and insulators allow or restrict the flow of electrons respectively.
- Current is the flow of electrons through a conductor. Voltage is the force that causes current to flow. Resistance opposes current flow.
- Ohm's law defines the relationship between current, voltage, and resistance in a circuit.
- Series circuits have one path for current to flow. The total resistance is the sum of individual resistances and the same current flows through each component.
Water is an important consideration for green building due to increasing water scarcity around the world. Buildings account for 20% of water usage, but efficiency strategies can achieve savings of 40%. Strategies include using native plants and drip irrigation for landscaping, low flow fixtures, water monitoring, rainwater harvesting, greywater recycling, and composting toilets. Concrete and steel are the largest material contributors for buildings, but timber and mass timber structures are alternatives that reduce embodied carbon by up to 75%. Life cycle analysis shows embodied carbon and energy can be reduced through material selection and use of sustainable sources like FSC timber.
The document discusses the history and properties of electricity and magnetism. It covers how electricity was first observed in amber, the development of theories on positive and negative charges by scientists like Du Fay and Franklin, and how static electricity works. It also explains concepts like conductors, insulators, charging and grounding objects, and Coulomb's law governing the electric force between charges.
Interactive textbook ch. 17 introduction to electricitytiffanysci
1) Friction and induction are the two main causes of static electricity.
2) Static electricity builds up in clouds during thunderstorms as water droplets, ice, and air move within the storm cloud, transferring negative charges.
3) Lightning rods help protect buildings by providing a path for the electric charges from lightning to safely move to the ground through the rod's wire connection.
This document discusses charge, lightning, and thunderstorms. It begins by defining electric charge and describing the three types of charges: positive, negative, and neutral. Charge can be transferred between objects through friction, conduction, or induction. Lightning is a large-scale electric spark that occurs during thunderstorms due to the buildup of charges in clouds. Earthing is the process of safely transferring excess charge from an object to the ground. During a thunderstorm, it is important to find shelter inside a building or vehicle and avoid open areas, tall objects, and water sources.
Interactive textbook ch. 18 sec 1 magnets & magnetismtiffanysci
Magnets have two poles, north and south, and exert magnetic forces on each other and other objects. Earth itself acts like a giant magnet, with its magnetic north pole located near its geographic south pole. Materials are magnetic if their atomic domains are aligned, allowing their magnetic fields to combine. There are different types of magnets including permanent and electromagnets. Earth's rotation creates electric currents in its liquid outer core, generating the planet's magnetic field.
Electrostatics is the study of electric charges at rest and the forces between them. Electrical forces act over short distances and opposite charges attract while like charges repel based on Coulomb's law. Materials are classified as conductors or insulators based on how tightly bound their electrons are. Objects can be charged through contact/friction or induction and develop a non-uniform distribution of charge known as polarization. An electric field is created by a charged object and defined as the region in which a test charge would experience force, with field lines indicating direction. Electric potential energy is the energy a charge has based on its position in an electric field. Capacitors can store electric energy by separating opposite charges on conducting plates.
This document discusses static electricity and how objects become electrically charged. It describes three main ways that objects can become charged: 1) charging by friction, where electrons are transferred between two objects in contact with each other; 2) charging by conduction, where charge flows through a conducting material when it touches a charged object; and 3) charging by induction, where a charged object induces a charge in a nearby object without direct contact. The document also discusses properties of charges, insulators and conductors, electroscopes for detecting charge, lightning formation in clouds, and how a Van de Graaff generator works to produce high voltages.
An electroscope is a device used to test if an object is charged. It consists of a metal ball, rod and leaves. When neutral, the leaves stay together, but when charged, they repel each other. Charging can occur through contact or induction. Induction involves charging an object without direct contact by using a nearby charged object to move its electrons. Grounding provides a path for charges to travel to or from the ground.
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge.
Here are some examples of static electricity in our day to day life:
When we walk on a carpeted floor and getting shock when touching a door knob or any other metal object is one of the best examples of static electricity.
Clothes stuck to one another after being in the dryer is another example of static electricity.
Static electricity is caused by an imbalance of electric charges, usually electrons, on the surface of materials. When certain materials are rubbed together, electrons can be transferred, leaving one material with an excess of electrons and a negative charge, and the other with a deficit of electrons and a positive charge. These imbalanced charges attract or repel each other, causing phenomena like balloons sticking to walls or hair standing on end. Lightning is a large-scale example of static electricity, where the bottoms of thunderclouds become negatively charged and the tops positively charged, until a discharge occurs as lightning.
The document summarizes static electricity and different models that were proposed to explain it. It discusses the two-fluid model proposed by Charles Dufay involving vitreous and resinous fluids. It then discusses Benjamin Franklin's one-fluid model involving positive and negative charges. Finally, it introduces the modern particle model involving electrons, protons and neutrons to explain how objects become charged through the gain or loss of electrons.
Electric charge is a fundamental property of matter that causes electromagnetic attraction and repulsion. The electric charge is quantized, meaning it occurs in discrete integer multiples of the elementary charge carried by a single electron or proton. Robert Millikan's oil drop experiment directly demonstrated the quantization of charge by measuring the electric charges on tiny oil droplets, finding they were always integer multiples of approximately 1.6×10^-19 coulombs. Coulomb's law describes the electric force between two charged particles, stating it is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Static electricity occurs when objects become electrically charged through the transfer of electrons. Charging occurs when two materials are rubbed together, causing electrons to move from one material to the other. This leaves one material with an excess of electrons and a negative charge, and the other material with a deficit of electrons and a positive charge. The electric charges remain on the surface of the objects until they are given a path to ground or neutralize each other through contact or discharge.
The document discusses different aspects of electric charge including:
1) Atoms contain protons, neutrons, and electrons. Objects with equal numbers of protons and electrons are neutral, while imbalances lead to electric charges.
2) Charged objects exert electric forces on each other - opposites attract and likes repel. The elementary charge unit is 1 electron or proton.
3) Neutral objects can become polarized when near a charged object, gaining opposite charges on opposite sides and becoming attracted to both positive and negative charges.
Electrons, protons, and neutrons are the main subatomic particles that make up atoms. Electrons have a negative charge and orbit the nucleus, while protons have a positive charge in the nucleus. Neutrons have no charge. Atoms consist of a nucleus surrounded by electrons. When an object gains or loses electrons through friction or contact with another object, it becomes positively or negatively charged respectively, as gaining or losing electrons leaves the object with an excess or deficit of protons. Charging by contact occurs when a charged object transfers charge to a neutral object they touch.
This document provides an overview of electricity and electrical engineering concepts. It discusses the following key points:
- Electricity is a fundamental property of nature that is observed and exploited, though not fully explained. It is a source of energy.
- Atoms are made up of protons, neutrons, and electrons. Protons are positively charged, electrons are negatively charged, and their interactions hold atoms together.
- Electric charge is a phenomenon associated with atomic particles. The fundamental unit of charge is the coulomb. Charged particles experience attractive or repulsive forces depending on whether their charges are opposite or alike.
- Electrons in atoms occupy discrete energy levels or bands. Insulators have a large gap between
Static electricity occurs when there is a build up of electric charge on the surface of a material without the flow of electric current. It results from the transfer of electrons between two materials during friction like rubbing a balloon on hair. This can cause attraction between materials with opposite charges like a negatively charged balloon and positively charged hair. Common examples are rubbing a plastic ruler to attract paper or walking on carpet and touching a doorknob to discharge. Different materials have different tendencies to gain or lose electrons through friction based on their electron affinity.
This document provides an overview of forces and motion. It discusses the four fundamental forces - strong nuclear, weak nuclear, electromagnetic, and gravitational. It explains how static electricity is caused by an imbalance of electrons on objects. Experiments are described to demonstrate the attraction and repulsion of charged objects. The document also covers electromagnetism, generators, motors, gravity, and Newton's laws of motion. Key concepts include like charges repelling and opposite charges attracting, and that in a vacuum all objects fall at the same rate regardless of mass.
A positive charge occurs when an object has fewer electrons than protons, giving it an excess of protons. This excess of protons causes a negative charge to accumulate on nearby objects, resulting in an attractive electrostatic force. Positive charges are used to generate electric currents and in applications like spray painting. A negative charge is an excess of electrons, causing the object to attract other positively charged particles. Neutral objects have an equal number of protons and electrons, resulting in no net electric charge.
This document provides an overview of basic electricity concepts including:
- Conductors and insulators allow or restrict the flow of electrons respectively.
- Current is the flow of electrons through a conductor. Voltage is the force that causes current to flow. Resistance opposes current flow.
- Ohm's law defines the relationship between current, voltage, and resistance in a circuit.
- Series circuits have one path for current to flow. The total resistance is the sum of individual resistances and the same current flows through each component.
Water is an important consideration for green building due to increasing water scarcity around the world. Buildings account for 20% of water usage, but efficiency strategies can achieve savings of 40%. Strategies include using native plants and drip irrigation for landscaping, low flow fixtures, water monitoring, rainwater harvesting, greywater recycling, and composting toilets. Concrete and steel are the largest material contributors for buildings, but timber and mass timber structures are alternatives that reduce embodied carbon by up to 75%. Life cycle analysis shows embodied carbon and energy can be reduced through material selection and use of sustainable sources like FSC timber.
The document discusses the history and properties of electricity and magnetism. It covers how electricity was first observed in amber, the development of theories on positive and negative charges by scientists like Du Fay and Franklin, and how static electricity works. It also explains concepts like conductors, insulators, charging and grounding objects, and Coulomb's law governing the electric force between charges.
This document provides an introduction to a green building course. It defines green buildings as those that are designed and built in an efficient and environmentally friendly manner. It discusses the importance of sustainable built environments in the context of issues like urbanization, energy and waste in Vietnam, and climate change risks. Finally, it outlines some current ideas and movements in green building, including life cycle considerations, sustainable materials, biomimicry, high performance facades, transit oriented development, renewable energy, ecological and social sustainability, and vernacular architecture.
1) The document discusses momentum, including its definition as mass times velocity (p=mv), examples of equivalent momenta between objects with different masses and speeds, and the impulse-momentum theorem relating impulse (force times time) to changes in momentum.
2) Conservation of linear momentum is explained, stating that the total momentum of an isolated system is constant. Examples show applying this principle to calculate velocities after collisions.
3) The proof of conservation of momentum relies on Newton's Third Law and the cancellation of internal action-reaction force pairs between objects, leaving the net external force on the overall system as zero.
Image result for Electrical circuits
An electric circuit is a path in which electrons from a voltage or current source flow. The point where those electrons enter an electrical circuit is called the "source" of electrons.
1. Mesh analysis is a technique to analyze circuits using loops or meshes. It involves defining meshes, applying Kirchhoff's voltage law, and solving for mesh currents.
2. Once the mesh currents are solved for, they can be used to calculate the voltage across each component using Ohm's law.
3. The key steps of mesh analysis are to identify all meshes in the circuit, label currents and voltages, write KVL equations, and solve to find mesh currents and component voltages.
1. Atoms contain negatively charged electrons that orbit the positively charged nucleus, which contains positively charged protons and uncharged neutrons.
2. Static electricity occurs when an object gains an excess of electrons or protons, causing it to become charged. Charged objects exert forces on other charged objects, attracting or repelling them.
3. Lightning is a large discharge of static electricity that builds up in storm clouds. The flash of light is produced by collisions between electrons and air molecules, and the thunderous sound comes from rapidly expanding heated air.
This document introduces key concepts in electrical circuits including complex and polar forms of representation, phase representation of real and imaginary terms, the 'J' and 'a' operators, the relation between voltage and current in resistors, inductors and capacitors, equivalent circuits, network elements, types of sources, Kirchhoff's laws, nodal analysis and mesh analysis, the relation between impedance and admittance, practical and ideal sources, source transformation, and the power triangle.
Potential energy is energy that is stored and waiting to be used, and it comes in three main forms: gravitational potential energy due to an object's position, elastic potential energy from compression/expansion, and chemical potential energy stored in chemical bonds. Kinetic energy is the energy an object has due to its motion and is calculated as one-half the mass times the velocity squared. The document divides all energy into either potential energy or kinetic energy.
This document provides an overview of Circuit Theory (EE102) Lecture 1, covering basic concepts in electric circuits including:
- Systems of units used to measure electric properties like current and voltage.
- Basic circuit elements like resistors, sources, and nodes and branches.
- Kirchhoff's laws and techniques for analyzing series and parallel circuits.
- Transformations between wye and delta networks.
Worked examples are provided to illustrate applying concepts like Ohm's law, Kirchhoff's laws, and calculating equivalent resistances for series and parallel circuits.
This document provides an introduction to semiconductor materials. It discusses three types of electronic materials: conductors, insulators, and semiconductors. Semiconductors are able to allow or suppress electrical current depending on conditions. The document explains intrinsic and extrinsic semiconductors, how doping with impurities transforms a semiconductor into an n-type or p-type material. It also covers crystal lattice structures, band structures, carrier concentrations and conductivity in semiconductors. Optical and photoconductive properties of semiconductors are briefly discussed.
Here are the steps to solve this parallel circuit problem:
1. To find the equivalent resistance Req, use the parallel formula:
1/Req = 1/2.4 + 1/6 + 1/4
1/Req = 0.41667
Req = 2.4 Ω
2. To find the total current Itotal, use Ohm's Law:
V = IReq
15 = 2.4Itotal
Itotal = 6.25 A
3. The voltage across each resistor is 15 V (same in parallel).
Use Ohm's Law to find the current through each:
Imiddle = V/R = 15/6 = 2.5 A
I
This document provides an overview of direct current (DC) circuits and circuit analysis techniques. It defines key concepts like voltage sources, current sources, ideal and real sources, and dependent and independent sources. It also explains Kirchhoff's laws, nodal analysis, and mesh analysis. Kirchhoff's current law states that the algebraic sum of currents at a node is zero. Kirchhoff's voltage law states that the algebraic sum of voltages in a closed loop is zero. Nodal analysis uses Kirchhoff's current law to set up equations relating node voltages. Mesh analysis uses Kirchhoff's voltage law to set up equations relating mesh currents.
The document discusses different types of energy, dividing energy into potential energy which is stored energy that can later be used, and kinetic energy which is the energy of motion. It specifically describes gravitational potential energy as energy due to an object's position, calculated using mass x gravity x height, and kinetic energy as energy due to an object's motion, calculated using half mass x velocity squared. The document emphasizes that energy is never created or destroyed, but only changes form, so the total energy in a system remains conserved as potential energy changes to kinetic energy and vice versa.
This document outlines a lecture on electrostatics. It will cover electrical forces and charges, conservation of charge, Coulomb's law, conductors and insulators, superconductors, charging, charge polarization, electric field, electric potential, and electric energy storage. Key concepts include that opposite charges attract and like charges repel, Coulomb's law describes the relationship between electrical force and charge, conductors allow electron flow while insulators do not, and capacitors can store electrical energy between charged plates.
The document provides an overview of key concepts in electricity and magnetism including:
1) Positive and negative charge, Coulomb's law, and the forces between charged objects.
2) What charge is and that protons and electrons have equal but opposite charges.
3) Conductors, insulators, semiconductors, and their properties related to charge flow.
4) Electromagnets, magnetic fields generated by electric currents, and their applications.
5) Electromagnetic induction, transformers, alternating current, and direct current.
This is a ppt which is based on electricity chapter of class 10 in science ncert cbse book . it will definitely enhance your knowledge and clear all concepts about this chapter .
Kirchhoff's rules provide a means of obtaining enough independent equations to solve for currents in an electrical circuit. They were first described in 1845 by German physicist Gustav Kirchhoff and consist of two equalities: (1) the Junction Rule states that the sum of currents entering a junction equals the sum leaving, based on conservation of charge, and (2) the Loop Rule states that the sum of voltages around a closed conducting loop must be zero, based on conservation of energy. Kirchhoff's rules can be applied to traffic flow analysis and are the basis of circuit simulation software used in integrated circuit design.
This document discusses electric fields and forces. It explains that electric charge comes from electrons and protons in atoms, and that rubbing materials together can transfer electrons, creating a separation of positive and negative charges. It also describes how conductors, insulators, and semiconductors differ in how easily they allow charge to flow through or remain separated.
This document defines static electricity and electric charges. It explains that atoms become charged when they gain or lose electrons, making them more positive or negative. Electrons can be easily removed from atoms, while protons are very difficult to remove. Charging occurs through friction, contact, or induction as electrons are transferred between objects. Conductors allow charge to spread evenly, while insulators trap charges on their surface. Grounding neutralizes charged objects by allowing electrons to flow to or from the earth.
This document discusses electricity and electric charge. It defines the basic properties of electric charge including that there are two types - positive and negative. Like charges repel and opposite charges attract. Charge is conserved and cannot be created or destroyed. The key particles - proton, electron, and neutron - and their charges are identified. Conductors allow charge to move through them while insulators restrict charge movement. Triboelectric series shows how charge transfers during friction. Induction can charge objects without contact by redistributing protons and electrons. Devices like electroscopes and Van de Graaff generators are used to study electric charge.
This document introduces the topics of static electricity, current electricity, and power generation. It discusses what causes static electricity, such as walking across carpet and touching something to get a shock. Static electricity occurs when electrons are not moving along a path but rather build up as they move between atoms. The document also covers electric charge, conductors, insulators, and tools for detecting electric charge like electroscopes.
- Electric charge exists in two types, positive and negative, and is quantized in units of the elementary charge e. Charges of the same type repel, while opposite charges attract.
- Coulomb's law describes the electrostatic force between two point charges, directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
- The electric field is defined as the force per unit charge exerted on a test charge at some point, and can be used to determine the force on any charge. Electric fields from multiple sources add through superposition.
This document provides an outline for a lesson on static electricity. It begins with a review of atomic structure and defines key terms like electricity, charge, and friction. It explains how friction can separate charges by moving electrons between objects. This creates static electricity. Insulators and conductors are introduced, as well as the triboelectric series. The document discusses concepts like polarization and the laws of charges. It provides examples of static electricity experiments and classifications of materials as conductors and insulators.
This document provides an overview of electrostatics and how electric charges behave. It discusses that matter is made up of protons, neutrons, and electrons which can gain or lose electrons, becoming positively or negatively charged. It describes how like charges repel and unlike charges attract. Conductors, insulators, and semiconductors are introduced based on how easily their outer electrons can move. Methods of charging objects such as friction, conduction, induction, and more are explained. An electroscope is presented as a device to detect electric charge.
The document discusses electric charge and its properties. It states that electric charge is an intrinsic property of protons and electrons, with protons having a positive charge and electrons having a negative charge. The magnitude of the charge on a proton equals the magnitude of the charge on an electron. Like charges repel each other, while unlike charges attract. Charge is quantized and can only occur in integer multiples of the elementary charge e. The document also discusses how objects can become charged through rubbing, contact, or induction, and introduces Coulomb's law which describes the electric force between two point charges.
1. The document discusses the subatomic particles that make up atoms, including electrons, protons, and neutrons. It defines related terms like atomic number and mass number.
2. Atoms can form isotopes that have the same number of protons but different numbers of neutrons. The forces that hold atoms together are electric forces between the positively charged protons and negatively charged electrons.
3. Oppositely charged particles attract, while similarly charged particles repel, according to the rules of electric force. This balance of forces is what allows atoms to form without collapsing in on themselves or flying apart.
Here are the key points about electric fields based on the document:
- An electric field (E) represents the influence of an electric charge. It has magnitude and direction at each point in space.
- The direction of electric field lines indicates the direction of the electric force on a positive test charge placed at that point.
- The density of electric field lines indicates the strength of the electric field - more closely spaced lines means a stronger field.
- Electric field lines outside a conductor must be perpendicular to the conductor's surface because charges within a conductor redistribute such that the net electric field inside a conductor is always zero due to electrostatic equilibrium.
Static electricity is the buildup of electric charges on the surface of objects. It occurs through three main processes: friction, conduction, and induction. When certain materials are rubbed together, electrons are transferred, leaving one material with an excess of electrons and the other with a deficit. This separation of charges causes a static electric force. No new charges are created in this process - electrons simply move between objects. Conductors allow charge to flow easily while insulators do not, making insulators prone to charging. Grounding neutralizes charge by providing a path to earth. Lightning is a large-scale example of static discharge.
Electrostatics covers the properties of electric charges, electrostatic force, and electric fields. Key points include:
- There are two types of electric charges: positive and negative. Like charges repel and unlike charges attract.
- Charge is quantized and conserved. It exists in integer multiples of the fundamental unit, e.
- Coulomb's law describes the electrostatic force between two point charges. The force is proportional to the product of the charges and inversely proportional to the square of the distance between them.
- Electric fields are vector fields that exist around charged objects. The electric field strength is defined as the force per unit charge. Field lines are used to represent electric fields graphically.
This document provides an overview of direct current circuits and related concepts. It discusses the structure of atoms and how they can gain or lose electrons. It also describes the three main types of materials based on their ability to conduct electricity: conductors, semiconductors, and insulators. Additionally, the document defines key terms like voltage, electrostatic charge, and methods for producing voltage such as friction, pressure, and heat. Safety precautions for working with direct current circuits are also mentioned.
This document provides notes on electrostatics. It defines key terms like electrostatics, electric charge, conductors, insulators, semiconductors. It describes properties of electric charge including additivity, quantization, and conservation. Coulomb's law is explained, relating the electrostatic force between two point charges to the product of their charges and the inverse square of the distance between them. The document also compares electrostatic force and gravitational force.
The document discusses the history and properties of electricity and electric charge. It traces the key discoveries around electricity from ancient Greeks observing amber's attractive properties when rubbed in 600 BC to J.J. Thompson's discovery of the electron in 1890. When certain materials like glass are rubbed against other materials like silk, electrons are transferred, leaving one material with an excess of electrons and the other with a deficit. Like charges repel and opposite charges attract based on the inverse square law discovered by Coulomb in 1770. Electric charge is quantized and comes in positive or negative units of the elementary charge of an electron.
The document discusses the history and properties of electricity and electric charge. It describes how Greeks first discovered the attractive properties of amber in 600 BC and key discoveries throughout history that helped define positive and negative electric charge. The document explains how rubbing certain materials like glass and silk can cause the transfer of electrons, leaving one material with an excess of electrons and the other with a deficit. It summarizes that electric charge is a fundamental property of matter that can be either positive or negative, and like charges repel while opposite charges attract.
Electric Charge and Static Electricity PPT.pptxMarkJayAquillo
This document discusses electric charge and static electricity. It explains that atoms contain positively charged protons, neutral neutrons, and negatively charged electrons. The law of electric charges states that like charges repel and opposite charges attract. Objects can become charged through friction, conduction, or induction by gaining or losing electrons. Conductors allow charge to flow easily while insulators do not. Static electricity occurs when a stationary electric charge builds up on an object. Lightning forms when built-up electric charges in clouds discharge to the ground.
Electric Charge and Static Electricity PPT (1).pptxMarkJayAquillo
This document discusses electric charge and static electricity. It explains that atoms contain positively charged protons, neutral neutrons, and negatively charged electrons. The law of electric charges states that like charges repel and opposite charges attract. Objects can become charged through friction, conduction, or induction by gaining or losing electrons. Conductors allow charge to flow easily while insulators do not. Static electricity occurs when a stationary electric charge builds up on an object. Lightning forms when built-up charges in clouds discharge to the ground.
This document provides an introduction to basic electrical and electronics concepts. It discusses how electricity is present in nature and how mankind has harnessed it for use. It then covers atomic structure, defining elements, compounds, and molecules. Models of the atom including Dalton's, Rutherford's, and Bohr's are explained. The document also discusses electrons, protons, neutrons, and their roles. Energy shells and electron quotas are defined. Finally, the document introduces concepts of electric charge, static electricity, and the coulomb unit of charge.
1. The document provides a refresher on basic differentiation techniques for powers, constants, sums, differences, and other terms.
2. It reviews rules for differentiating simple and general powers, constants, sums and differences of terms, and powers multiplied by constants.
3. Examples and practice problems are provided for each technique to help the reader practice the skills.
This document contains information about different types of waves including mechanical waves, electromagnetic waves, and gravitational waves. It discusses key wave properties such as amplitude, wavelength, frequency, period, and speed. It also covers topics like longitudinal and transverse wave motion, reflection, refraction, and standing waves. Examples are provided to illustrate wave phenomena in various contexts like sound waves, water waves, and seismic waves.
This document discusses concepts related to thermodynamics including:
- Kinetic molecular theory explains heat in terms of molecular motion rather than a fluid called "caloric."
- Internal energy is the sum of kinetic and potential energy of all particles in a substance due to their motion and interactions. Temperature is proportional to average kinetic energy.
- Heat is the transfer of thermal energy between objects of different temperature, while internal energy is the thermal energy contained within an object.
- Thermal equilibrium occurs when objects are at the same temperature so there is no net heat transfer between them. Heat transfer can occur via conduction, convection, or radiation.
Sound waves are longitudinal waves that propagate through a medium by causing oscillations in pressure. The speed of sound depends on properties of the medium like density and bulk modulus. Frequency determines pitch, with the human hearing range from 20-20,000 Hz. The Doppler effect causes changes in observed frequency due to relative motion between source and receiver. Sonar uses echoes to locate objects by sound, while sonic booms occur when the source moves at or faster than the speed of sound.
Optics involves the reflection and refraction of light. Reflection occurs when light bounces off a surface, following the law of reflection where the angle of incidence equals the angle of reflection. Refraction is when light changes speed and direction when passing from one medium to another due to a change in index of refraction. Refraction is described by Snell's law, where the ratio of sines of the incident and refracted angles is equal to the ratio of the indices of refraction. Total internal reflection occurs when light passes from a higher to lower index of refraction beyond the critical angle and is completely reflected rather than refracted.
The magnetic field is weak above the top wire of the current loop because the top and bottom lengths of wire produce magnetic fields in opposite directions (one into the page and one out of the page), which cancel each other out. So at a point directly above the wire, the net magnetic field is small.
Here are the key differences between primary colors in light vs pigments:
- Primary light colors are red, green, and blue. These can be combined to form white light.
- Primary pigment colors are yellow, cyan, and magenta. These absorb one primary light color and reflect the other two.
- Secondary light colors are formed by combining two primary light colors: orange (red + green), violet (red + blue), and yellow (green + blue).
- Secondary pigment colors are formed by absorbing two primary light colors: red (absorbs yellow and cyan), blue (absorbs yellow and magenta), and green (absorbs cyan and magenta).
So in summary, primary
The document discusses several key concepts related to fluids, including:
1) States of matter, phase changes, density, pressure, and Archimedes' principle.
2) Pressure in fluids depends on depth and density, not the shape of the container, according to the formula P=ρgh.
3) Pascal's principle states that pressure changes are transmitted undiminished throughout an enclosed fluid.
1. The document discusses electric fields, including field vectors, field strengths for point charges and uniform fields, and fields around various charge configurations.
2. It reviews gravitational fields and compares them to electric fields. Both fields are defined by the force per unit charge or mass exerted on a test particle.
3. Examples are given of calculating field strengths and drawing electric field lines for single and multiple point charges of the same and opposite signs.
Newton's Law of Gravitation and Kepler's Laws of Planetary Motion describe gravity and orbital motion. Newton's Law states that the gravitational force between two objects is proportional to their masses and inversely proportional to the square of the distance between them. Kepler's Laws state that planets move in ellipses with the Sun at one focus, sweep out equal areas in equal times, and have periods proportional to the 3/2 power of their distances from the Sun.
The document discusses projectile motion, describing how objects moving through the air are affected by gravity. It explains that gravity only affects vertical motion, not horizontal motion, so horizontally a projectile maintains a constant velocity if no other forces are present. Examples are provided to demonstrate how to calculate the time of flight, range, and landing point of projectiles fired at various angles and velocities.
mg sinθ - μk mg cosθ = ma
So, a = (mg sinθ - μk mg cosθ) / m = g(sinθ - μk cosθ)
The acceleration depends on the angle and the coefficient of
kinetic friction.
This document discusses Newton's laws of motion and provides examples of forces. It introduces Newton's three laws, including inertia, Fnet=ma, and action-reaction. Examples are given for each law such as an astronaut drifting in space (1st law), graphs of force vs. acceleration (2nd law), and collisions between objects of different masses (3rd law). Common forces like gravity, tension, and normal forces are also explained.
This document provides an overview of key physics concepts related to kinematics including:
- Vectors and scalars
- Displacement, distance, velocity, acceleration, and their relationships
- Mass vs weight
- Motion graphs including position, velocity, and acceleration graphs
- Kinematics equations for constant acceleration including relationships between displacement, velocity, acceleration, and time
- Sample kinematics problems and explanations of concepts like uniform acceleration are provided.
1. Electrostatics
Electric charge Van de Graff generators
Conservation of charge Equilibrium problems
Insulators & conductors Grounding
Charging objects Static electricity
Electroscopes Coulomb’s law
Lightning Systems of charges
2. Electric Charge
• Just as most particles have an attribute known as mass, many
possess another attribute called charge. Charge and mass are intrinsic
properties, defining properties that particles possess by their very
nature.
• Unlike mass, there are two different kinds of charge: positive and
negative.
• Particles with a unlike charges attract, while those with like charges
repel.
• Most everyday objects are comprised of billions of charged, but
usually there are about the same number of positive charges as
negative, leaving the object as a whole neutral.
• A charged object is an object that has an excess of one type of
charge, e.g., more positive than negative. The amount of excess
charge is the charge we assign to that object.
3. Conservation of Charge
Charged particles can be transferred from one object to another, but the total
amount of charge is conserved. Experiments have shown that whenever
subatomic particles are transferred between objects or interact to produce
other subatomic particles, the total charge before and after is the same (along
with the total energy and momentum). Example: An object with 5 excess
units of positive charge and another with 2 units of excess negative charge
are released from rest and attract each other. (By Newton’s 3rd law, the forces
are equal strength, opposite directions, but their accelerations depend on
their masses too.) Since there is no net force on the system, their center of
mass does not accelerate, and they collide there. As they “fall” toward each
other, electric potential energy is converted to kinetic energy. When contact
is made charge may be exchanged but they total amount before and after
must be the same. After the collision the total momentum must still be zero.
Before After
+5 -2 +1.5 +1.5
Total charge: +3 Total charge: +3
4. Conservation of Charge: β-decay
• The stability of the nucleus of an atom depends on its size and its
proton-neutron ratio. This instability sometimes results in a
radioactive process known as β-decay.
• A neutron can turn into a proton, but in the process an electron
(beta particle) is ejected at high speed from the nucleus to conserve
charge.
• A proton can turn into a neutron. In this case the beta particle is an
positron (an antielectron: same mass as an electron but a positive
charge) to make up for the loss of positive charge of the proton.
• In either case, charge, momentum, and energy are conserved.
5. SI unit of Charge: the Coulomb
• Just as we have an SI unit for mass, the kilogram, we have one
for charge as well. It’s called the coulomb, and its symbol is C.
• It’s named after a French physicist, Charles Coulomb, who did
research on charges in the mid and late 1700’s.
• A coulomb is a fairly large amount of charge, so sometimes
we measure small amounts of charge in μC (mircocoloumbs).
• An electron has a charge of -1.6 × 10-19 C.
• A proton has a charge of +1.6 × 10-19 C.
• In a wire, if one coulomb of charge flows past a point in one
second, we say the current in the wire is one ampere.
6. Elementary Charge
• Charges come in small, discrete bundles. Another way to say this
is that charge is quantized. This means an object can possess
charge in incremental, rather than continuous, amounts.
• Imagine the graph of a linear function buy when you zoom in
very close you see that it really is a step function with very small
steps.
• The smallest amount of charge that can be added or removed
from an object is the elementary charge, e = 1.6 × 10-19 C.
• The charge of a proton is +e, an electron -e.
• The charge of an object, Q, is always a multiple of this
elementary charge: Q = N e, where N is an integer.
• How many excess protons are required for an object to have 1 C
of charge?
7. Insulators vs. Conductors
• A conductor is a material in which excess charge freely flows.
Metals are typically excellent conductors because the valence (outer
shell) electrons in metal atoms are not confined to any one atom.
Rather, they roam freely about a metal object. Metal are excellent
conductors of electricity (and heat) for this reason.
• An insulator is a material in which excess charge, for the most
part, resides where it is deposited. That is, once placed, it does not
move. Most nonmetallic material are good insulators. Valence
electrons are much more tightly bound to the atoms and are not free
to roam about. Insulators are useful for studying electrostatics (the
study of charge that can be localized and contained).
• Semi-conductors, like silicon used in computer chips, have
electrical conductivity between that of conductors and insulators.
Details on Conductors, Semiconductors, and Insulators
8. Electrons and Chemical Bonds
All chemical bonding is due to forces between electrostatic charges.
Covalent bonding: A pair of electrons is shared between two
nonmetal atoms, allowing each atom to have access to enough
electrons to fill its outer shell. Except for hydrogen, this usually
means 8 electrons in the outer shell (octet rule).
Ionic bonding: One or more valence electrons of a metal atom are
“stolen” by a nonmetal atom, leaving a positive metal ion and a
negative nonmetal ion, which then attract one another.
Metallic bonding: Valence electrons of metals flow freely throughout
a metal object. These delocalized electrons are attracted to the nuclei
of the atoms through which they are moving about. This produces a
strong binding force that holds the atoms together. In an iron bar, for
example, there is no covalent or ionic bonding. Metallic bonding hold
the metal together.
9. Charging up Objects
Charging up an object does not mean creating new charges. Charging
implies either adding electrons to an object, removing electrons from
an object, or separating out positive and negative charges within an
object. This can be accomplish in 3 different ways:
• Friction: Rubbing two materials together can rub electrons off of
one and onto the other.
• Conduction: Touching an object to a charged object could lead to a
flow of charge between them.
• Induction: If a charged object is brought near (but not touching) a
second object, the charged object could attract or repel electrons
(depending on its charge) in the second object. This yields a
separation charge in the second object, an induced charge separation.
10. Electroscopes
An electroscope is an apparatus comprised of a metal sphere and
very light metal leaves. A metal rod connects the leaves to the
Electroscopes
sphere. The leaves are enclosed in an insulating, transparent
container. When the electroscope is uncharged the leaves hang
vertically. The scope is charged by placing a charged rod near the
sphere. The rod is charged by friction. If a rubber rod is rubbed
with fur, electrons will be rubbed off the fur and
onto the rubber rod, leaving the rod negatively
charged. If a glass rod is rubbed with silk,
electrons will be rubbed off the rod onto the silk,
leaving the glass rod positively charged. Either
rod, if brought near, will charge the scope by
induction. Also, either rod, if contact is made
with the sphere, will charge the scope by
conduction.
uncharged continued…
11. Electroscopes (cont.)
When a positively charged rod is placed near but not touching the
metal sphere, some of the valence electrons in the metal leaves are
drawn up into the sphere, leaving the sphere negatively charged and
the leaves positively charged. Thus, the rod has induced a charge
separation in the scope. The light,
++++++++++++++ positive leaves repel each other and
separate. The electroscope as a whole
- --
-- - is still electrically neutral, but it has
- undergone a charge separation. As
soon as the rod is removed from the
vicinity, the charge separation will
+ + cease to exist and the leaves the drop.
+ + Note: Only the electron are mobile;
+ + the positives on the leaves represent
missing electrons.
continued…
12. Electroscopes (cont.)
When a negatively charged rod is placed near but not touching the
metal sphere, some of the valence electrons in the sphere are repelled
down into the metal leaves, leaving the sphere positively charged and
the leaves negatively charged. The rod has again induced a charge
separation in the scope. The light,
------------------- negative leaves repel each other as
before. Again, the electroscope as a
++ whole is electrically neutral, but the
+ +
++
charge separation will remain so long
as the rod remains nearby. Note that
this situation is indistinguishable from
- - the situation with the positive rod.
- - Since the effects are the same, how do
- - we know that the rods really do have
different charges?
continued…
13. Electroscopes (cont.)
Now let’s touch the negative rod to the sphere. Some of the electrons
can actually hop onto the sphere and spread throughout the scope.
This is charging by conduction since, instead of rearranging charges
in the scope, new charges have been added; the scope is no longer
neutral. The extra electrons force the leaves apart, even when the rod
is removed. If the negative rod returns, it charges the leaves further,
but this time by induction (by driving some of ----------------
electrons on the sphere down
- - - -
- - to the leaves). This causes an - -
- -
increased separation of the
leaves. When the rod is
removed, the scope will return
- - to the state on the left. - -
- -
- - Continued… - -
- - - -
extra e- ’s added leaf spread increases
14. Electroscopes (cont.)
The pic on the left shows a scope that has acquired extra electrons
from a negative rod that has since been removed. Now we bring a
positive rod nearby. This has the opposite effect of bringing the
negative rod near. This time some of the extra electrons in the leaves
head to the sphere and the spread of the leaves diminishes. Note: the
scope is still negatively charged overall, but the presence of the
positive rod means more of the +++++++++++
- -
excess negative charge will - -
- - reside in the sphere and less in - -
- - - -
the leaves. When the rod is
removed, the scope return to
the state on the left.
- - - -
Continued…
- - - -
- - - -
extra e- ’s added leaf spread decreases
15. Grounding an Electroscope
Whether a scope has charged by conduction, either positively or
negatively, the quickest way to “uncharge” it is by grounding it. To
do this we simply touch the sphere. When a negatively charged scope
is grounded by your hand, the excess electrons from the scope travel
into your body and, from there, into your surroundings. When a
positively charged scope is
- grounded, electrons from your -
-
-
- body flow into the scope until -
- - it is neutral. Your surroundings ++
- - + +
- - ++
will replace the electrons
you’ve donated to the scope.
As always, it’s only the
- - electrons that move around. + +
- - + +
- - + +
16. Electroscope Practice Problem
For the following scenario, try to predict what would happen after
each step. Explain each in terms of electrons and charging.
1. A rod is rubbed with a material that has a greater affinity for
electrons than the rod does.
2. This rod is brought near a neutral electroscope.
3. This rod touches the electroscope and is removed.
4. A positive rod is alternately brought near and removed.
5. A negative rod is alternately brought near and removed.
6. Finally, you touch the scope with your finger.
17. Redistributing Charge on Conducting Spheres
Two neutral spheres, A & B, are placed side by side, touching. A negatively
charged rod is brought near A, which induces a charge separation in the “A-B
system.” Some of the valence e-’s in A migrate to B. When the rod is re-
moved and A & B are separated, A is +, B is -, but the system is still neutral.
--- +Q -Q
A B A B
A is now brought near neutral sphere C, inducing a charge separation on it.
Valence e-’s in C migrate toward A, but since C is being touched on the
positive side, e-’s from the hand will move into C. Interestingly, C retains a
net negative charge after A and the hand are removed even though no
charged object ever made contact with it.
+Q -
A C C
18. Static Electricity: Shocks
If you walk around on carpeting in your stocking feet, especially in
the winter when the air is dry, and then touch something metal, you
may feel a shock. As you walk you can become negatively charged
by friction. When you make contact with a metal door knob, you
discharge rapidly into the metal and feel a shock at the point of
contact. A similar effect occurs in the winter when you exit a car: if
you slide out of your seat and touch then touch the car door, you
might feel a shock.
The reason the effect most often occurs in winter is because the air is
typically drier then. Humidity in the air can rather quickly rob excess
charges from a charged body, thereby neutralizing it before a rapid,
localized discharge (and resulting shock) can take place.
Care must be taken to prevent static discharges where sensitive
electronics are in use or where volatile substances are stored.
19. +- # 1
Static Electricity: Balloons
+-
+- Pic #1: If you rub a balloon on your hair,
electrons will be rubbed off your hair onto the
+-
balloon (charging by friction).
+- Pic #2: If you then place the negatively
charged balloon near a neutral wall, the
+- - -- balloon will repel some of the electrons near it
-
- - #2 in the wall. This is inducing a charge
+- - - separation in the wall. Now the wall, while
still neutral, has a positive charge near the
+- balloon. Thus, the balloon sticks to the wall.
-+ Pick #3: Your hair now might stand up. This
-+ is because it has been left positively charged.
#3
-+ As with the leaves of a charged electroscope,
the light hairs repel each other.
20. Hanging Balloons
#1
You hang two balloons from the
ceiling and rub them on your hair.
#2
When you move out of the way, the negatively charged balloons
repel each other. On each balloon there are three forces: tension
in the string, gravity, and the electric force. The angle of
separation will grow until equilibrium is achieved (zero net
force).
#3
If you move your head close to either
of the balloons, it will move toward
you since your hair remains positively
charged.
21. Polarization of a Cloud
Lightning is the discharge of static electricity on a
massive scale. Before a strike the bottom part of a
cloud becomes negatively charged and the top part
positively charged. The exact mechanism by which
this polarization (charge separation) takes place is
uncertain, but this is the precursor to a lightning
strike from cloud to cloud or cloud to ground.
One mechanism incorporates friction: when moist, warm air rises, it cools and
water droplets form. These droplets collide with ice crystals and water droplets
in a cloud. Electrons are torn off the rising water droplets by the ice crystals.
The positive droplets rise to the top of the cloud, while the negative ice crystals
remain at the bottom.
A second mechanism involves the freezing process: experiments have shown
that when water vapor freezes the central ice crystal becomes negatively
charged, while the water surrounding it becomes positive. If rising air tears the
surrounding water from the ice, the cloud becomes polarized.
There are other theories as well.
Detailed Lightning Diagrams
22. Lightning Strikes
+ + + + ++++
The negative bottom part of the cloud induces +
a charge separation in the ground below. Air is
normally a very good insulator, but if the charge - -- --
separation is big enough, the air between the
- - - -
cloud and ground can become ionized (a
plasma). This allows some of the electrons in
the cloud to begin to migrate into the ionized air
below. This is called a “leader.” Positive ions
from the ground migrate up to meet the leader.
This is called a “streamer.” As soon as the
leader and streamer meet, a fully conductive
path exists between the cloud and ground and a
+ +
lightning strike occurs. Billions of trillions of + +
electrons flow into the ground in less than a +
millisecond. The strike can be hotter than the
surface of the sun. The heat expands the
surrounding air; which then claps as thunder.
+ + + +
23. Lightning Rods and Grounding
Discovered by Ben Franklin, a lightning rod is a long, pointed, metal
pole attached to a building. It may seem crazy to attract lightning
close to a susceptible structure, but a lightning rod can afford some
protection. When positive charges accumulate beneath a cloud, the
accumulation is extremely high near the tip of the rod. As a result, an
electric field is produced that is much greater surrounding the tip
than around the building. (We’ll study electric fields in the next
unit.) This strong electric field ionizes the air around the tip of the
rod and “encourages” a strike to occur there.
If a strike does occur, the electricity travels down the rod into a
copper cable that connects the lightning rod to a grounding rod
buried in the earth. There the excess charge is grounded, i.e., the
electrons are dissipated throughout the landscape. By taking this
route, rather than through a building and its wiring, much loss is
prevented.
24. Van de Graaff
Generator
A Van de Graaff generator consists of a large metal dome attached to a tube, within
which a long rubber belt is turning on rollers. As the belt turns friction between it and
the bottom roller cause the e-’s to move from the belt to the roller. A metal brush then
drains these e-’s away and grounds them. So, as the belt passes the bottom roller it
acquires a positive charge, which is transported to the top of the device (inside the
dome). Here another metal brush facilitates the transfer of electrons from the dome to
the belt, leaving the dome positively charged.
In short, the belt transports electrons from a metal dome to the ground, producing a
very positively charged dome. No outside source of charge is required, and the
generator could even be powered by a hand crank. A person touching the dome will
have some of her e-’s drained out. So, her lightweight, positive hair will repel itself.
Coming close to the charge dome will produce sparks when electrons jump from a
person to the dome.
Internal workings Detailed explanation
25. Coulomb’s Law
There is an inverse square formula, called Coulomb’s law, for finding
the force on one point charge due to another:
K q1 q2
F= K = 9 × 109 N m2 / C2
r2
This formula is just like Newton’s law of uniform gravitation with charges
replacing masses and K replacing G. It states that the electric force on
each of the point charges is directly proportional to each charge and
inversely proportional to the square of the distance between them. The
easiest way to use the formula to ignore signs when entering charges, since
we already know that like charges repel and opposites attract. K is the
constant of proportionality. Its units serve to reduce all units on the right to
nothing but newtons. Forces are equal but opposite.
+ F r F-
q1 q2
Charges in Motion Coulomb's Law Detailed Example
26. Electric Force vs. Gravitational Force
K q1 q2
FE = K = 9 × 109 N m2 / C2
r2
G m1 m2
FG = G = 6.67 × 10-11 N m2 / kg2
r2
Gravity is the dominant force when it comes to shaping galaxies and the
like, but notice that K is about 20 orders of magnitude greater than G.
Technically, they can’t be directly compared, since they have different
units. The point is, though, that a whole lot of mass is required to produce
a significant force, but a relatively small amount of charge can overcome
this, explaining how the electric force on a balloon can easily match the
balloon’s weight. When dealing with high-charge, low-mass objects, such
as protons & electrons, the force of gravity is negligible.
27. Electric Force Example
A proton and an electron are separated by 15 μm. They are released from rest.
Our goal is to find the acceleration each undergoes at the instant of release.
1. Find the electric force on each particle. 1.024 × 10-18 N
2. Find the gravitational force on each particle. A proton’s mass is
1.67 × 10-27 kg, and an electron’s mass is 9.11 × 10-31 kg.
4.51 × 10-58 N
3. Find the net force on each and round appropriately. Note that the
gravitational force is inconsequential here. 1.024 × 10-18 N
4. Find the acceleration on each particle.
e-: 1.124 × 1012 m/s2, p+: 6.13 × 108 m/s2
5. Why couldn’t we use kinematics to find the time it would take
the particles to collide? r changes, so F changes, so a changes.
+ 15 μm +
28. System of 3 Charges
In a system of three point charges, each charge exerts a forces on the
other two. So, here we’ve got a vector net force problem. Find the net
force on charge B. Steps:
1. Find the distance in meters between A and B
using the law of cosines. 0.261947 m
A
2. Find angle B in the triangle using the law of +3 μC
sines. 36.027932 º
3. Find FBA (the magnitude of the force on charge
0.786981 N
17 cm
B due to charge A).
4.591836 N
4. Find FBC.
115º
5. 3.78 N (right) , forces on B into components
Break up the 1.25 N (up) C
and find the net horiz. & vertical forces. B -5 μC
3.98 N at 14 cm
18.3 º N of E +2 μC
29. System of 4 Charges
Here four fixed charges are arranged in a rectangle.
Find Fnet on charge D.
Solution: -16 µC +25 µC
A C
767.2 N at 59.6 º N of W
4 cm
B D
+9 µC 3 cm -7 µC
Link
30. Hanging Charge Problem
Two objects of equal charge and mass are θ
hung from the same point on a ceiling L L
with equally long strings. They repel each
other forming an angle θ between the strings. T
Find q as a function of m, L and θ.
FE q, m q, m
Solution: Draw a f.b.d. on one of the
objects, break T into components, and mg
write net vertical and horiz. equations:
T sin(θ / 2) = FE , T cos(θ / 2) = mg.
Dividing equations and using Coulomb’s law yields:
mg tan(θ / 2) = FE = Kq 2 / r 2, where r = 2 L sin(θ / 2). Thus,
q= 4 L2 mg tan(θ / 2) sin2(θ / 2)
K
31. Point of Equilibrium
Clearly, half way between two equal charges is a point of equilibrium,
P, as shown on the left. (This means there is zero net force on any
charge placed at P.) At no other point in space, even points equidistant
between the two charges, will equilibrium occur.
Depicted on the right are two positive point charges, one with twice
the charge of the other, separated by a distance d. In this case, P must
be closer to q than 2 q since in order for their forces to be the same,
we must be closer to the smaller charge. Since Coulomb’s formula is
nonlinear, we can’t assume that P is twice as close to the smaller
charge. We’ll call this distance x and calculate it in terms of d.
Continued…
x=?
+q P +q +q P +2 q
d
32. Point of Equilibrium (cont.)
Since P is the equilibrium point, no matter x
what charge is placed at P, there should be
zero electric on it. Thus an arbitrary “test P
+q +2 q
charge” q0 (any size any sign) at P will feel
a force due to q and an equal force due to
2 q. We compute each of these forces via d
Coulomb’s law:
The K’s, q’s, and q0’s cancel, the latter
K q q0 K (2 q) q0 showing that the location of P is
= independent of the charge placed there.
x 2
(d - x) 2
Cross multiplying we obtain:
(d - x)2 = 2 x 2 ⇒ d 2 - 2 x d + x 2 = 2 x 2
⇒ x 2 + 2 x d - d 2 = 0.
33. x
Point of Equilibrium (cont.)
+q P +2 q
From x 2 + 2 x d - d 2 = 0,
the quadratic formula yields: d
-2 d ± (2 d )2 - 4 (1) (-d 2 ) -2 d ± 8d2
x= =
2 (1) 2
= -d ± d 2 Since x is a distance, we choose the positive root:
x = d ( 2 - 1 ) ≈ 0.41 d. Note that x < 0.5 d, as predicted.
Note that if the two charges had been the same, we would have
⇒ d 2 - 2 x d + x 2 = x2
started with (d - x)2 = x 2
⇒ d 2 - 2 x d = 0 ⇒ d (d - 2 x ) = 0 ⇒ x = d / 2, as
predicted. This serves as a check on our reasoning.
34. Equilibrium with Several Charges
Several equal point charges are to be arranged in a plane so that another point
charge with non-negligible mass can be suspended above the plane. How might this
be done?
Answer: Arrange the charges in a circle, spaced evenly, and fix them in place.
Place another charge of the same sign above the center of the circle. If placed at
the right distance above the plane, the charge could hover. This arrangement works
because of symmetry. The electric force vectors on the hovering charge are shown.
Each vector is the same magnitude and they lie in a cone. Each vector has a vertical
component and a component in the plane. The planar components cancel out, but
the vertical components add to negate
the weight vector. Continued…
35. Equilibrium with Several Charges (cont.)
Note that the charges in the plane are fixed. That is, they are attached somehow in
the plane. They could, for example, be attached to an insulating ring, which is then
set on a table. Regardless, how could the arrangement of charges in the plane be
modified so as to maintain equilibrium of the hovering charge but allow it to hover
at a different height?
Answer: If the charges in the plane are arranged in a circle with a large radius, the
electric force vectors would be more horizontal, thereby working together less and
canceling each other more. The hovering charge would lower. Since its weight
doesn’t change, it must be closer to the plane in order to increase the forces to
compensate for their partial cancellation. If the charges in the plane were arranged
in a small circle, the vectors would be more vertical, thereby working together
more and canceling each other less. The hovering charge would rise and the vectors
would decrease in magnitude. To maximize the height of the hovering charge, all
the charges in the plane should be brought to a single point. Continued…