Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the Nano second range. If the radiation source has the duration of 2 ns and the number of photons emitted during the pulse source is 2.5 × 1015, calculate the energy of the source.
Given:
Period, T = 2 ns
Frequency, v = [1] / T
= [1] / [2.0 × 10–9]
= 0.5 × 109 Hz
By Planck’s relation we have,
Energy, E = n× h×v
Where
n = number of photons
h = Planck’s constant
E = [2.5× 1015] × [6.626× 10-34] × [0.5× 109]
= 8.28× 10-10 J
Therefore, the energy of the photon is 8.28× 10-10 J.