Electric Current: Solved Example Problems

EXAMPLE 2.2

If an electric field of magnitude 570 N C-1, is applied in the copper wire, find the acceleration experienced by the electron.

Solution:

E = 570 N C-1, e = 1.6 × 10-19 C, m = 9.11 × 10-31 kg and a = ?

F = ma = eE

a = eE/m = 570×1 .6×10−19/9 .11×10-31 

= 912 ×10−19 Ã—1031 / 9 .11

= 1.001 × 1014 m s-2

EXAMPLE 2.3

A copper wire of cross-sectional area 0.5 mm2 carries a current of 0.2 A. If the free electron density of copper is 8.4 × 1028 m-3 then compute the drift velocity of free electrons.

Solution

The relation between drift velocity of electrons and current in a wire of cross-sectional area A is

vd = I/ ne A 

vd = 0.03 x 10-3 m s-1

EXAMPLE 2.4

Determine the number of electrons flowing per second through a conductor, when a current of 32 A flows through it.

Solution

I = 32 A , t = 1 s

Charge of an electron, e = 1.6 × 10-19 C

The number of electrons flowing per second, n =?

I = q/t = ne/t

n = It/e

n = 32×1 / 1 .6×10−19 C

n = 20 × 1019 = 2 × 1020 electrons