Page 4 - Electrostatics 11

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.

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
☻ 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.

ii) Insulators: A material which does not allow charges to move in it is called
an insulator. E.g., non-metals, glass, rubber, plastics, paper, dry wood,
mica, porcelain, dry air, ebonite etc.
iii) Semiconductors: A material which behaves as conductors under certain

physical conditions is called semiconductors. E.g., silicon, germanium,
carbon etc.

Electrification: The process of charging a body positively or negatively by
transfer of electrons in the outermost orbits from one body to the other.

4 Electrostatics