Question

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 a duration of 2 ns and the number of photons emitted during the pulse source is 2.5 × 1015, calculate the energy of the source.

Answer 1

Frequency of radiation, v = $\frac{1}{2.0\times10^{-9}}$ s
= 5.0 × 108 s
Energy (E) of source = Nh$\omega$
Where N = number of photons emitted
h = Planck's constant
$\omega$ = frequency of radiation
Substituting the values in the given expression of (E):
E = (2.5 × 1015) (6.626 × 10-34 Js) (5.0 × 108 s-1)
E = 8.282 × 1010 J
Hence, the energy of the source (E) is 8.282 × 1010 J.