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# Electric Current: Solved Example Problems

Physics : Current Electricity: Electric Current: Solved Example Problems

### EXAMPLE 2.1

Compute the current in the wire if a charge of 120 C is flowing through a copper wire in 1 minute.

Solution

The current (rate of flow of charge) in the wire is

I = Q/t = 120/60 = 2A

### 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 ├Ś 10-19 C, m = 9.11 ├Ś 10-31 kg and a = ?

F = ma = eE

a = eE/m = 570├Ś1 .6├Ś10ŌłÆ19/9 .11├Ś10-31

= 912 ├Ś10ŌłÆ19 ├Ś1031 / 9 .11

= 1.001 ├Ś 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 ├Ś 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 ├Ś 10-19 C

The number of electrons flowing per second, n =?

I = q/t = ne/t

n = It/e

n = 32├Ś1 / 1 .6├Ś10ŌłÆ19 C

n = 20 ├Ś 1019 = 2 ├Ś 1020 electrons

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12th Physics : Current Electricity : Electric Current: Solved Example Problems |