Page 4 - Electrostatics 11 class

Grade 11 © GC Shiba

Electricity: The branch of physics which deals with charges either at rest or in
motion is called electricity. There are two branches of electricity.

1. Electrostatics: The branch of electricity that deals with a charge at rest. This

is also called frictional electricity as the charges are produced on a body due
to the friction.
2. Current electricity: The branch of electricity that deals with a charge in
motion.

Electric charge: It is defined as the product of electric current and time for which
this current persists.
i.e., q = I.t

Types of charges: There are 2 types of charge produced on the body.
1. Positive charge: When a glass rod is rubbed with a silk cloth, then the rod
acquires positive charges. Here the electrons transfer from the glass rod to
the silk. So, the rod becomes +ve charged while the silk becomes -ve

charged.
2. Negative charge: When an ebonite rod is rubbed with fur or funnel, then the
rod acquires negative charge. Here, the electrons transfer from the fur to the

ebonite. So, the rod becomes -ve charged while the fur becomes +ve charged.
Properties of charge:
☻ Electric charge exists either positive or negative.

☻ Like charges repel and unlike charges attract.
☻ It is a scalar quantity.
☻ Electric charge is additive. The total electric charge of a body is the algebraic

sum of all charges on it.
☻ It is quantized. It means charge is always an integral multiple of basic charge
e (charge of an electron).
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i.e., Q = ± n e ; where n is an integer and e = -1.6 × 10 C.
☻ Total charge in an isolated system remains constant. This is called the
principle of conservation of charge.
☻ The electric charge on a body doesn't depend on its speed.

☻ SI unit of charge is coulomb (ampere sec).
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☻ CGS unit of charge is stat coulomb ( 1 C = 3 × 10 stat coulomb ).

Conductors and insulators:

i) Conductor: A material which allows charge to move in it due to free
electrons is called conductor. E.g., silver, copper, carbon in the form of
charcoal and graphite, coal, acid, alkali, salt , earth human body etc.

4 Electrostatics