Two sources of light each with a power 200 W emit radiations of wavelength 10 nm and 600 nm, respectively. The ratio of number of photons emitted per second from two sources of photons, respectively will be:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1 : 60
The power of a source is the energy emitted per second, which is the number of photons emitted per second n multiplied by the energy of one photon \( E = hc/\lambda \).
\( \displaystyle P = nE = n\,\frac{hc}{\lambda} \Rightarrow n = \frac{P\lambda}{hc} \)
Both powers are equal, so \( n\propto\lambda \).
\( \displaystyle \frac{n_1}{n_2} = \frac{\lambda_1}{\lambda_2} = \frac{10\,\mathrm{nm}}{600\,\mathrm{nm}} = \frac{1}{60} \)