Question

Two bulbs '$A$' and '$B$' emit red light and yellow light at $8000\,\mathring{A}$ and $4000\,\mathring{A}$; respectively. The number of photons emitted by both the bulbs per second is the same. If the red bulb is labelled as $100\, W$, find the wattage of the yellow bulb.

Answer 1

Let energy of photon coming of bulbs $A$ and $B$ are, respectively, $E_{A}$ and $E_{B}$. Thus,
$E_{A}=\frac{12400}{8000} eV$ and $E_{B}=\frac{12400}{8000} eV$
Number of photons emitted per second is same.
Let. wattage of $2\, nd$ bulb $B\, W$, hence
$\frac{12400}{8000} \times n eV =100 \times 1$
$\frac{12400}{4000} n eV =W \times 1$
$\Rightarrow 100 \times 8000=W \times 4000$
$\Rightarrow W=200\, W$