Calculate the number of photons in $6.62 \mathrm{J}$ of radiation energy of frequency ${10}^{12} \mathrm{Hz}$. Given $h=6.62\times {10}^{-34} \mathrm{Js}$.

Energy of each photon is

$E=h\nu =6.62\times {10}^{-34}\times {10}^{12}=6.62\times {10}^{-22} \mathrm{J}$

Number of photons present in $6.62 \mathrm{J}$ of radiation energy is 

$N=\frac{E}{h\nu }=\frac{6.62}{6.62\times {10}^{-22}}={10}^{22}$