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) $3 \times 10^{20}$
Concept. Photons per second $= \dfrac{P}{hc/\lambda}$.
Step 1. Photon energy. $3.3 \times 10^{-19}$ J.
Step 2. Number. $\dfrac{100}{3.3 \times 10^{-19}} \approx 3 \times 10^{20}$.
Answer. $3 \times 10^{20}$ (Option B).
Solution by Sreeraj P, M.Sc Physics