Question

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

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

Answer 1

The correct option is B $8A$

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

To find the current flowing

Solution:

no of electrons,$n=2\times {10}^{21}$

Average drift speed, $=0.25mm/s$

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

where $Q=ne$ (no of electrons $\times$ charge on an electron)

we get $Q=2\times {10}^{21}\times 1.6\times {10}^{-19}=3.2\times {10}^2$

$\text{Time}=\frac{\text{distance}}{\text{speed}}⟹\text{time}=\frac{10}{0.25}=40s$

substituting the values,

$I=\frac{3.2\times {10}^2}{40}⟹I=8A$

is therequired current flowing through the wire