A photon has a wavelength of 500 nm. (a) Find its momentum…

Step 1. The momentum. $p = \dfrac{h}{\lambda} = \dfrac{6.63 \times 10^{-34}\ \text{J s}}{500 \times 10^{-9}\ \text{m}} = 1.33 \times 10^{-27}\ \text{kg m/s}$.

Step 2. The photon energy. $E = \dfrac{1240\ \text{eV nm}}{500\ \text{nm}} = 2.48\ \text{eV}$.

Step 3. The electron. $K = \dfrac{p^2}{2m} = \dfrac{(1.33 \times 10^{-27}\ \text{kg m/s})^2}{2 \times 9.1 \times 10^{-31}\ \text{kg}} = 9.7 \times 10^{-25}\ \text{J}$. In eV, $\dfrac{9.7 \times 10^{-25}}{1.6 \times 10^{-19}} = 6.04 \times 10^{-6}\ \text{eV}$.