# 23. How many photons are emitted per second by a 5 mW laser source operating at 632.8 nm?

Arun
25758 Points
4 years ago
the energy of each photon is =
E = hc / $\lambda$
= 6.63 * 10 –34 * 3 * 108 / 632.8 * 10 –9
= 3.14 * 10 –19  J
the energy emitted per second by the laser is =  5 * 10 –3  J
hence totla no. of photons emitted per second  = 5 * 10 –3  J / 3.14 * 10 –19  J
= 1.6 * 1016