Question

There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1 nm and the other visible light of 500 nm. The ratio of number of photons of X-rays to the photons of visible light of the given wavelength is:

• A. 1:500
• B. 1:400
• C. 1:300
• D. 1:200

Answer 1

The correct option is A 1:500

Here, $P=100W,{\lambda }_1=1nm,{\lambda }_2=500nm$

Let $n_1$ and $n_2$ be the number of photons of X-rays and visible light emitted from the two sources
$\therefore$ $n_1\frac{hc}{{\lambda }_1}=n_2\frac{hc}{{\lambda }_2}$ or

$\frac{n_1}{{\lambda }_1}=\frac{n_2}{{\lambda }_2}$n or $\frac{n_1}{n_2}=\frac{{\lambda }_2}{{\lambda }_2}=\frac{1}{500}$