Question

(a) Define electric current. What is its S.I. unit? Is it a scalar or a vector quantity? What is the direction of electric current?

(b) How many electrons flowing per second should flow to produce a current of 1A?

Answer 1

(a) Electric current: The flow of charge in a definite direction constitutes the electric current and the rate of flow of charge through any cross-section of a conductor is the measure of current i.e.,

= \(\frac{\text { Total charge flowing(q)} }{\text { Time taken (t)}}\) 

If dq charge is flowing through a section of a conductor in time dt, the electric current is given by

I = \(\frac{dq}{dt}\)  ..........................(1)

Unit of electric current. S.I. unit of current is ampere. It is also called practical unit of current. It is denoted by A,

1 ampere (A) = \(\frac{1 \text { Coulomb } }{1 \text { second } }\) =  = 1 C s^-1

Thus the current through a wire is said to be 1 ampere if one Coulomb of charge is flowing per second through a section of the wire.

Current is a scalar quantity, the direction of flow of positive charges is considered as conventional direction of current.

In solids, positive charges being heavy do not move and current is due to free electrons, therefore, conventional direction of current is opposite to electronic current.

(b) I = \(\frac{q}{t} = \frac{ne}{t}\)

n = \(\frac{It}{e} = \frac{1\times1}{1.6\times10^{-19}}\)

= 6.25 x 10¹⁸ electrons per second.