Q. The number of photons of wavelength $540\ nm$ emitted per second by an electric bulb of power $100\ W$ is (taking $h = 6 \times 10^{- 34}J$-$s$)
A) 100
B) 1000
C) $3 \times 10^{20}$
D) $3 \times 10^{18}$
Explanation
(c) $p = \frac{nhc}{\lambda t} \Rightarrow 100 = \frac{n \times 6 \times 10^{- 34} \times 3 \times 10^{8}}{540 \times 10^{- 9} \times 1} \Rightarrow n = 3 \times 10^{20}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.