Page 29 - Basic Electrical Engineering

negative charge. Since there are equal number of protons and electrons in an
atom, an atom is basically neutral in nature.
If from a body consisting of neutral atoms, some electrons are removed,

there will be a deficit of electrons in the body, and the body will attain
positive charge. If neutral atoms of a body are supplied some extra electrons,

the body will attain negative charge. Thus, we can say that the deficit or
excess of electrons in a body is called charge.

Charge of an electron is very small. Coulomb is the unit of charge. The
charge of an electron is only 1.602 × 10 −19 Coulomb (C). Thus, we can say

that the number of electrons per Coulomb is the reciprocal of 1.602 × 10 −19
18
which equals approx. 6.28 × 10 electrons. Therefore, charge of 6.28 × 10 18
electrons is equal to 1C. When we say that a body has a positive charge of
18
1C, it is understood that the body has a deficit of 6.28 × 10 electrons.
Any charge is an example of static electricity because the electrons or
protons are not in motion. You must have seen the effect of charged particles
when you comb your hair with a plastic comb, the comb attracts some of your

hair. The work of combing causes friction, producing charge of extra
electrons and excess protons causing attraction.

Charge in motion is called electric current. Any charge has the potential of
doing work, i.e., of moving another charge either by attraction or by

repulsion. A charge is the result of separating electrons and protons. The
charge of electrons or protons has potential because it likes to return back the

work that was done to produce it.

1.3 CONDUCTORS, INSULATORS, AND SEMICONDUCTORS
The electrons in an atom revolve in different orbits or shells. The shells are

named as K, L, M, N, etc. The number of electrons that should be in a filled
2
inner shell is given by 2n where n is shell number 1, 2, 3, 4, etc. starting
from the nearest one, i.e., first shell to the nucleus. If n = 1, the first shell will
contain two electrons. If n = 2, the second shell will contain eight electrons.

This way, the number of electrons in the shells are 2, 8, 18, 32, etc. The filled
outermost shell should always contain a maximum number of eight electrons.