ELECTRIC CHARGE

Electric charge is defined as an intrinsic property of the elementary particles of matter. It is the electric charge that gives rise to the electric force between objects. It is represented by the symbol q. The SI unit of electric charge is coulomb (C).

A body is said to be charged if it has either extra electrons or some electrons are missing from it. If the body has excess of electrons, then it is said to be negatively charged and if it has deficiency of electrons, then it is said to be positively charged. Therefore, when a body is negatively charges, its mass increases (because it gains electrons) and when a body is positively charged, its mass decreases because it loses electrons.

Charge and mass of elementary charge

An electron has a negative charge (-e) and a proton has a positive charge (+e), where e = 1.60218 x 10-19 C. The mass of an electron is 9.1 x 10-31 kg and the mass of a proton is 1.67 x 10-27 kg.

Some important points regarding electric charge

1. Like charges attract each other and unlike charges attract each other.

2. If a body possesses a net electric charge, then it is said to be charged or electrified. If it has no net charge, then it is said to be neutral. For example, an atom is electrically neutral because it has no net charge, i.e. the number of electrons in an atom is equal to the number of protons present in it.

3. Charge is a scalar quantity and it can be of two types, i.e. negative and positive.

4. Charge is invariant, i.e. it does not depend upon the velocity of the charged particle.

5. A charged particle at rest produces electric field. A charged particle in an non-accelerated motion produces both electric and magnetic field but it doesn’t radiate energy. But, an accelerated particle produces electric and magnetic field as well as radiates energy in the form of electromagnetic waves.

6. 1 coulomb = 3 x 109 esu = 0.1 emu of charge (esu means electrostatic unit and emu means electromagnetic unit)

Can a proton attract another proton ?

Two protons repel each other due to the electrostatic force of repulsion between them and they attract each other because of the gravitational force of attraction. Also, when the distance between two protons is less than or equal to 10-15 m, then the nuclear force comes into play and hence they start attracting each other.