Question

A 100 watt bulb emits monochromatic light of wavelength 400 nm. Calculate the number of photons emitted per second by the bulb.

Answer 1

E = \(\frac{hc}{\lambda}\)

= \(\frac{6.626\times10^{-34}Js\times3\times10^8m^{-1}}{400\times10^{-9}}\)

= 4.969 × 10⁻¹⁹J

Power of the bulb = 100watt = 100Js⁻¹

Number of Photons emitted

= \(\frac{100\,Js^{-1}}{4.969\times10^{-19}J}\)

= 2.012 × 10²⁰ Photons.