Question

Find the number of photons emitted per second by a 25W source of monochromatic light of wavelength 6000Å.

Answer 1

Energy of photon

E = hv = \(\frac{hc}{\lambda} = \frac{6.6 \times 10^{-34}\times 3 \times 10^8}{6000 \times 10^{-10}}\)

So number of photons emitted per second by 25W source

n = \(\frac{25W \times1_s}{3.3 \times 10^{-19}J}\)

or n = 7.57 x 10¹⁹.