Q 12-11-026NEETJEE MainMedium
A $100$ W source emits light of wavelength $600$ nm. The number of photons it emits per second is ($h = 6.6 \times 10^{-34}$ J s)
Answer: (B) $3 \times 10^{20}$
$E = \dfrac{hc}{\lambda} = \dfrac{6.6 \times 10^{-34} \times 3 \times 10^8}{6 \times 10^{-7}} = 3.3 \times 10^{-19}$ J. $n = \dfrac{100}{3.3 \times 10^{-19}} \approx 3 \times 10^{20}$ per second.
Solution by Sreeraj P, M.Sc Physics