devarshi-dt-logo

Question:

A bulb is emitted electromagnetic radiation of 660nm wavelength. The total energy of radiation is 3 × 10⁻¹⁸ J. The number of emitted photons will be: (h = 6.6 × 10⁻³⁴ J⋅s, C = 3 × 10⁸ m/s)

1

10

100

1000

Solution:

Correct option is B. 10

Number of photons = n
E = hc/λ
3 × 10⁻¹⁸ = (6.6 × 10⁻³⁴ × 3 × 10⁸ × n) / (660 × 10⁻⁹)
n = 30/3 = 10