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 is `2.5xx10^(15)`, calculate the energy of the source.

Explanation

Frequency `= (1)/(2 xx 10^(-9) s) = 0.5 xx 10^(9) s^(-1)`
Energy `= N hv = (2.5 xx 10^(5)) (6.626 xx 10^(-34) Js) (0.5 xx 10^(9) s^(-1)) = 8.28 xx 10^(-10) J`