Question

A 100 W bulb radiates energy at rate of 100 J/s. If the light emitted has wavelength of 525 nm. How many photons are emitted per second?

(A) 1.51 × 10²⁰

(B) 1.51 × 10²²

(C) 2.64 × 10²⁰

(D) 4.5 × 10¹⁹

Answer 1

The correct option is (C) 2.64 × 10²⁰.

Explanation:

E_photon = E = (hc / λ)

= [{6.623 × 10^–34 × 3 × 10⁸} / {525 × 10^–9}]

= 0.037 × 10^–17 J

E_photon = 3.7 × 10^–19 J

Eradiated = 100 (J/s) × 1 s = 100 J

 ∴ No of photons = {(E_radiated) / (E_photon)}

∴ n = {100 / (3.7 × 10^–19)}

= 0.27 × 10²¹

= 2.7 × 10²⁰ photons per second