Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nanosecond range. If the radiation source has the duration of 2 \mathrm{~ns} and the number of photons emitted during the pulse source is 2.5 \times 10^{15} J, calculate the energy of the source.
Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nanosecond range. If the radiation source has the duration of 2 \mathrm{~ns} and the number of photons emitted during the pulse source is 2.5 \times 10^{15} J, calculate the energy of the source.

Frequency of radiation (\nu),
\nu=\frac{1}{2.0 \times 10^{-9} s}
\nu=5.0 \times 10^{8} s^{-1}
Energy (E) of source = Nhv
Where,
N is the no. photons emitted
\mathrm{h} is Planck’s constant
v denotes the frequency of the radiation
Substituting these values in the expression for (E):
\begin{array}{l} E=\left(2.5 \times 10^{15}\right)\left(6.626 \times 10^{-34} J s\right)\left(5.0 \times 10^{8} s^{-1}\right) \\ E=8.282 \times 10^{-10} J \end{array}
Hence, the energy of the source (E) is 8.282 \times 10^{-10} J.