Question

A $60\, W$ incandescent lamp operates at $120\, V$. 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 $P=60\, W$
Operating voltage $V =120\, V$
$\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 , $Q=I=\frac{1}{2} C$
$\Rightarrow n e=\frac{1}{2}$
where $e=$ electronic charge,
and $n=$ number of electrons.
$\therefore n=\frac{1}{2 e}=\frac{1}{2 \times 1.6 \times 10^{19}}$
$=3.12 \times 10^{18}$