What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy?

Energy of one photon, 

$\begin{array}{rl}\mathrm{E}& =\frac{\mathrm{hc}}{\mathrm{\lambda }}=\frac{6.626\times {10}^{-34}\mathrm{Js}\times 3.0\times {10}^8{\mathrm{ms}}^{-1}}{4000\times {10}^{-12}\mathrm{m}}\\ & (1\mathrm{pm}={10}^{-12}\mathrm{m})\\ & =4.9695\times {10}^{-17}\mathrm{J}\end{array}$

Number of photons, 

$\mathrm{N}=\frac{1\mathrm{J}}{4.9695\times {10}^{-17}\mathrm{J}}=2.0122\times {10}^{16}\text{ photons }$.