Question

A current of $1mA$ is flowing through a copper wire. How many electrons will pass a given point in one second. $[e=1.6\times {10}^{-19}coulomb]$

• A. $6.25\times {10}^{19}$
• B. $6.25\times {10}^9$
• C. $6.25\times {10}^{31}$
• D. $6.25\times {10}^{15}$

Answer 1

The correct option is D $6.25\times {10}^{15}$

$\text{Step 1: Quantization of charge}$

Let $n$ be the number of electrons passing through the wire.

We know that charge is quantized,

$q=ne$ $......\left(1\right)$

$\text{Step 2: Current flowing through the wire}$

$I=\frac{q}{t}$

From equation $\left(1\right)$

$I=\frac{ne}{t}$

$\Rightarrow n=\frac{It}{e}$

$\Rightarrow n=\frac{{10}^{-3}A\times 1s}{1.6\times {10}^{-19}C}$$=6.25\times {10}^{15}electrons$

Hence, the correct option is D.