Question

The number of free electrons per $10$ mm ordinary copper wire is about $2\times {10}^{21}$. The average drift speed of the electrons is $0.25$ mm current flowing is:

• A. $0.8$ A
• B. $8$ A
• C. $80$ A
• D. $5$ A

Answer 1

The correct option is B $8$ A

Given,

Number of electron, $n=2\times {10}^{21}$

Average drift speed, $0.25mm/s$

$Q=ne$

$Q=2\times {10}^{21}\times 1.6\times {10}^{-19}$

$Q=320C$

Since,

$s=\frac{D}{T}$

$T=\frac{D}{s}$

$T=\frac{10}{0.25}=40$

So, current

$I=\frac{Q}{T}$

$I=\frac{320}{40}$

$I=8A$