Question

A $60W$ incandescent lamp operates at $120V$. The number of electrons passing through the filament per second will be

• A. $1.61\times 10^{12}$
• B. $3.12\times 10^{18}$
• C. $7.21\times 10^{12}$
• D. $12.40\times 10^{13}$

Answer 1

Answer: (B)

The power of the incandescent lamp $P=60W$
Operating voltage $V=120V$
$\therefore$ Current through the filament $I=\frac{P}{V}$
$=\frac{60}{120}=\frac{1}{2}A$
Now $Q=1\times t$
For $t=1$ sec , $Q=I=\frac{1}{2}C$
$\Rightarrow ne=\frac{1}{2}$
where $e=$ electronic charge,
and $n=$ number of electrons.
$\therefore n=\frac{1}{2e}=\frac{1}{2\times 1.6\times 10^{19}}$
$=3.12\times 10^{18}$