Question

A 150 W lamp emits light of the mean wavelength of 5500 Å. If the efficiency is 12%, find out the number of photons emitted by the lamp in one second.

Answer 1

P = 150 W

λ = 5500 × 10⁻¹⁰ m

Efficiency = 12%

N = `("P"λ)/"hc"`

= `(150 xx 5500 xx 10^-10)/(6.626 xx 10^-34 xx 3 xx 10^8)`

= `(825 xx 10^-7)/(19.878 xx 10^-26)`

= 41.5 × 10¹⁹

Number of photons emitted is with 12% efficiency = `41.5 xx 10^19 xx 12/100`

N = 4.98 × 10¹⁹