General Physics

1. General Physics 2
Quarter 3 – Module 1
Electric Charge and Electric Field

2. • Lesson 1 – Electric Charge
• Lesson 2 – Coulomb’s Law
• Lesson 3 – Electric Forces and Electric Field

3. Lesson 1 – Electric Charge
Electricity
• The term electricity came from the Greek work elektron, or amber. It is
given the name electricity by Sir Wilhelm Gilbert because amber had
been the first substance known by the ancients to exhibit electrification
by rubbing.
• A plastic comb rubbed with a piece of fur can attract little bits of paper.
This ability to attract resembles that of a magnet. However, the
attraction of magnets is limited to objects made of iron, while amber
attracts all substances. This attractive force is known as electrostatic
force.

4. Lesson 1 – Electric Charge
1.1 Law of Charges
• Atoms have electric charges inside them. In the center of each atom is the nucleus.
• Nucleus is made up of protons (carriers of positive charges) and neutrons (uncharged
particles).
• In the outer part of the atom are found the orbiting electrons (carriers of negative
charges).
Precise value of the mass:
• Proton = 1.67262171(29) x 10−27 kg
• Electron = 9.1093826(16) x 10−31 kg
• Neutron = 1.67492728(29) x 10−27 kg
Precise value of the magnitude of charge:
• Electron or Proton =
e =1.60217653(14) x 10−19Coulomb, C

5. Lesson 1 – Electric Charge
When a plastic comb is rubbed with fur and held near a pith ball, the pith ball is
attracted to the comb. The pith ball swings away from the comb after touching the comb.
If a glass rod rubbed with silk is brought near the pith ball, it will react just as it did with
the comb. It was contended that something, a charge, had been added to the comb or the
rod to attract the pith ball. This charge is called an electric charge.
The experiments described above and many others like them have shown that
there are exactly two kinds of electric charges: the kind on the plastic comb rubbed with
fur and the kind on the glass rod rubbed with silk. Benjamin Franklin (1706-1790)
suggested calling these two kinds of charge negative and positive, respectively, and these
names are still used. The plastic rod and the silk have negative charge; the glass rod and
the fur have positive charge.

6. Lesson 1 – Electric Charge
Therefore:
Two positive charges or two negative charges
repel each other. A positive charge and a negative
charge attract each other.

7. Lesson 1 – Electric Charge

8. Lesson 1 – Electric Charge
1.1.1 Electric Charge is Conserved
1. Principle of conservation of charge:
“The algebraic sum of all electric charges in any closed system is constant.”
If we rub together a plastic rod and a piece of fur, both initially uncharged, the
rod acquires a negative charge (since it takes electrons from the fur) and the fur
acquires a positive charge of the same magnitude (since it has lost as many electrons
as the rod has gained). Hence the total electric charge on the two bodies together
does not change. In any charging process, charge is not created nor destroyed; it is
merely transferred from one body to another.

9. Lesson 1 – Electric Charge
1.1.1 Electric Charge is Conserved
2. Second principle is:
“The magnitude of charge of the electron or proton is a natural unit of charge.”
Every observable amount of electric charge is always an integer multiple of
this basic unit. We say that charge is quantized. A familiar example of quantization is
money. When you pay cash for an item in a store, you have to do it in one-cent
increments. Cash cannot be divided into amounts smaller than one cent, and electric
charge cannot be divided into amounts smaller than the charge of one electron or
proton.

10. Lesson 1 – Electric Charge
1.2 CONDUCTORS AND INSULATORS
Electric charges are more easily moved in some materials. This characteristic led
to the classification of materials into two groups – conductors and insulators.
• Materials whose electric charges are free to move within are called conductors.
• In some materials, electric charges are not free to move within. Such materials are
called insulators.

11. Lesson 1 – Electric Charge
“Most metals are good conductors, while most nonmetals are insulators.”
Within a solid metal such as copper, one or more outer electrons in each atom
become detached and can move freely throughout the material. The motion of these
negatively charged electrons carries charge through the metal. The other electrons
remain bound to the positively charged nuclei, which themselves are bound in nearly
fixed positions within the material.
In an insulator there are no, or very few, free electrons, and electric charge
cannot move freely through the material. Some materials called semiconductors are
intermediate in their properties between good conductors and good insulators. Certain
materials known as superconductors become perfect conductors at very low
temperatures.

12. Lesson 1 – Electric Charge
1.3 TYPES OF CHARGING
1.3.1 Charging by Conduction
Conductors can be charged by conduction. Conduction is
the transfer of electrons from a charged object to another
object by direct contact. In the conduction process, a body with
one type of charge produces the same type of charge on a
conductor.

13. Lesson 1 – Electric Charge
1.3 TYPES OF CHARGING
1.3.1 Charging by Conduction

14. Lesson 1 – Electric Charge
1.3 TYPES OF CHARGING
1.3.2 Charging by Induction
Induction is the movement of electrons to one part of an
object by the electric field of another object. In the induction
process, the opposite type of charge is produced.

15. Lesson 1 – Electric Charge
1.3.2 Charging by
Induction

16. Lesson 1 – Electric Charge
Important key points:
• Electric charges – proton (positive charge) and electron (negative charge)
• Opposite charges – attract
• Like charges – repel
• Conductors – materials has free movement of electric charges
Examples: mostly metal materials
• Insulators – materials does not allow the movement of electric charges
• Principles of Charging
1st principle - charge is not created nor destroyed
2nd principle - electric charge cannot be divided into amounts smaller
than the charge of one electron or proton
• Types of Conduction
1. Charging by Conduction - transfer of electrons from a charged object to
another object by direct contact
2. Charging by Induction - movement of electrons to one part of an object by
the electric field of another object

17. Lesson 1 – Electric Charge
Assignment: (To be submitted on Thursday, February 1, 2024)
Instruction: Answer the following questions. Write your answer in a
clean sheet of intermediate or yellow paper.
1. How do particles with the same charge react? How about the
unlike charge? Why?
2. What are the two ways of charging? Briefly explain each way.

18. Lesson 2 – Coulomb’s Law

19. Lesson 2 – Coulomb’s Law
• When dealing with charge objects, we also talk of forces between them.
These forces can either be attractive or repulsive.
• The electrostatic force also called Coulomb’s force that can be defined as
the amount and direction of attraction or repulsion between two
charged bodies.
• The law states that the magnitude of the electric force between two point
charges is directly proportional to the product of the charges and
inversely proportional to the square of the distance between them.

20. Lesson 2 – Coulomb’s Law
𝑭𝒆 =
𝒌𝒒𝑸
𝒅𝟐
where:
𝑭𝒆 - electric force
𝒅 – distance between the objects
𝒒 𝑎𝑛𝑑 𝑸 – are the charges on the charge objects
𝒌 – constant ; Formula 𝑘 = 8.99 ∙ 109 𝑁∙𝑚2
𝐶2

21. Lesson 2 – Coulomb’s Law
Net Electric Force
between
Three Charges

22. Lesson 2 – Coulomb’s Law
TAKE NOTE:
microcoulomb = 𝜇𝐶 =× 10−6
𝐶
nanocoulomb = n𝐶 = × 10−9
𝐶
picocoulomb = p𝐶 = × 10−12
𝐶

23. Lesson 2 – Coulomb’s Law
Example 1:
Three charge particles are arranged in a line as
shown in the figure below: 𝒒𝑨 = −5 𝜇𝐶, 𝒒𝑩 =
+ 10𝜇𝐶, 𝒒𝑪 = −12 𝜇𝐶. Calculate the net electrostatic
force on 𝑞𝐵 due to the other two charges.
- -
+
6 cm 4 cm
A B C

24. Lesson 2 – Coulomb’s Law
Example 2:
Three point charges are in a straight line. Their
charges are 𝒒𝑨 = +8 × 10−9
𝐶 , 𝒒𝑩 = +6 × 10−9
𝐶, and
𝒒𝑪 = −5 × 10−9
𝐶. The distance between 𝒒𝑨 and 𝒒𝑩 is
12 cm and the distance between 𝒒𝑩 and 𝒒𝑪 is 24 cm.
What is the net electrostatic force on 𝒒𝑩 due to the other
charges?
+ -
+
A B C

25. Lesson 2 – Coulomb’s Law
Try this:
Three point charges are in a straight line. Their
charges are 𝒒𝑨 = −7.27 𝑛𝐶 , 𝒒𝑩 = +12.36 𝑛𝐶, and 𝒒𝑪 =
− 5.18 𝑛𝐶. The distance between 𝒒𝑨 and 𝒒𝑩 is 4 × 10−5
𝐶
meters and the distance between 𝒒𝑩 and 𝒒𝑪 is 7 × 10−5
𝐶
meters. What is the net electrostatic force on 𝒒𝑩 due to
the other charges?
- -
+
A B C