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 $100W$, find the wattage of the yellow bulb.

Answer 1

Answer: 200

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 $2nd$ bulb $BW$, hence
$\frac{12400}{8000}\times neV=100\times 1$
$\frac{12400}{4000}neV=W\times 1$
$\Rightarrow 100\times 8000=W\times 4000$
$\Rightarrow W=200W$