A monochromatic point source of light operates at a power of 60 W and emits light of wavelength 663 nm . Assuming 100 % efficiency in converting electrical power into light, what is the total number of photons emitted per second by the source? (Take Planck's constant h = 6.63 10⁻³⁴ J s and speed of light c = 3 10^8 m/s )

Step-by-step solution

Energy of a single photon is given by E = hc Substituting the given values: E = 6.63 10⁻³⁴ 3 10^8 663 10⁻⁹ E = 6.63 3 10⁻²⁶ 6.63 10⁻⁷ = 3 10⁻¹⁹ J The total power emitted by the source is P = 60 W = 60 J/s Let n be the number of photons emitted per second. Then P = nE n = P E = 60 3 10⁻¹⁹ n = 20 10¹⁹ = 2 10²⁰ Answer: 2 10²⁰