Question
The number of photons of light having wave number $$'x'$$ in $$10$$ $$J$$ of energy source is :
A.
$$10hcx$$
B.
$$\frac{{hc}}{{10x}}$$
C.
$$\frac{{10}}{{hcx}}$$
D.
$${\text{None of these}}$$
Answer :
$$\frac{{10}}{{hcx}}$$
Solution :
$$\eqalign{
& E = \frac{{nhc}}{\lambda } = nhc\bar v\left( {\because \,\,\bar v = \frac{1}{\lambda }} \right) \cr
& \therefore \,\,10 = nhc\bar v\,\,\,{\text{or}}\,\,\,n = \frac{{10}}{{hc\bar v}} = \frac{{10}}{{hcx}} \cr} $$