Find the energy of radiation having $7000 \ \mathring{A}$ and $400 \ nm$ wavelength. $\left( h = 6.62 \times 10^{-34} \ J \ s, c = 3 \times 10^8 \ m/s \right)$

The energy of a photon is given by $E = \frac{hc}{\lambda}$.
For $\lambda_1 = 7000 \ \mathring{A} = 7000 \times 10^{-10} \ m$:
$E_1 = \frac{6.62 \times 10^{-34} \times 3 \times 10^8}{7000 \times 10^{-10}} = 2.837 \times 10^{-19} \ J$.
For $\lambda_2 = 400 \ nm = 400 \times 10^{-9} \ m$:
$E_2 = \frac{6.62 \times 10^{-34} \times 3 \times 10^8}{400 \times 10^{-9}} = 4.965 \times 10^{-19} \ J$.