1. By Squadron Leader Zahid Mir CS&IT Department , Superior University
PHY-AP Electric Charge By
Squadron Leader Zahid Mir
CS&IT Department , Superior University

2. What is Electric Charge?
An intrinsic property of protons and electrons, which make up all matter, is electric charge.
Two types of electric charge, positive and negative; a proton has a positive charge, and an electron has a negative charge.
The vast amount of charge in an everybody object is usually hidden _ an object contains equal amounts of two kinds of charges.

3. The total deficiency or excess of electrons
in a body is known as its charge.

4. Charging an Object due to Friction
It is possible to transfer electric charge from
one object to another. Usually electrons are
transferred, and the body that gains
electrons acquires an excess of negative
charge. The body that loses electrons has
an excess of positive charge.
Rubbing plastic rod with silk makes plastic negatively charged.
Rubbing glass rod with fur makes glass rod positively charged.
During any process, the net electric charge of an entire isolated system remains constant (is conserved). This is referred to as the law of conservation of electric charge.

5. Interaction between charges
Charges interact with each other with the help of force of attraction or repulsion between them.
Charges can be either positive or negative (Benjamin Franklin 1709 – 1790)

6. Electrostatics
Branch of science which deals with the phenomena associated with charges at rest.

7. Laws of Electrostatics
First Law
Like charges of electricity repel each other, whereas unlike charges attract each other.
Second Law
The force exerted between two point charges is directly proportional to the product of their strength and inversely proportional to the square of the distance between them.

8. Unit of Charge In SI Units, the unit of charge is Coulomb (C) .
1 C = Charge of 6 x 1018 electrons
Charge on 1 electron = = 1.6 x C
6 x 1018
Definition of Coulomb
One Way In term of electrostatic force : If a charge exerts a force of N to another charge at a distance of 1 m apart, then the amount of that charge is 1C.
But the force between static charges is difficult to calculate.
Other Way In term of magnetic force between current carrying wires.

9. Quantization of charge
Transfer of charge from one object to another is not continuous but in terms of discrete elements.
Charges always exists in quantities that are integral multiples of a certain elementary quantity of charge ‘e’.
q = ne
where e = x C
An electron has a charge of e-
Whereas a proton has a charge of e+
Quantization
When the value of a property are restricted to discrete multiples of a basic quantity, we say that the property is quantized.

10. Conductors and Insulators
Not only can electric charge exist on an object, but it can also move through an object.
Substances that readily conduct electric charge are called electrical conductors.
Materials that conduct electric charge poorly are known as electrical insulators.
Semiconductors are materials that are intermediate between conductors and insulators

11. Conductors
Why copper rod cannot be charged if you rub it with fur keeping the rod in your hand?
Conductors contains a large number of conduction electrons ( 1023 free electrons per cm3).

12. Insulators
In case of charged comb and pieces of paper it is not possible for electrons to collect on one end of paper (as in the case of conductors). Instead electrons in the individual molecules in the bits of paper are repelled by the negatively charged comb and so electrons are partially located on the side of each molecule, that is away from the comb. In each molecule, the positive end is close to comb and feels a greater force of attraction to the comb. Polarization The separation of positive and negative charge in an isolated object under the influence of a nearby charged object is known as Polarization. At macroscopic level it occur in the case of copper rod and at microscopic level in the case of paper pieces.

13. Charging by Contact and by Induction
When we have a pathway through which electrons can flow between an object
and the Earth, the object is said to be electrically grounded.