Find the mass of a photon emitted by a sodium lamp (wavelength $\lambda = 5890 \ \mathring{A}$). How many times is this mass compared to the mass of an electron?

(N/A) The mass of a photon is given by the relation $m = \frac{h}{\lambda c}$.
Given: $h = 6.626 \times 10^{-34} \ J \cdot s$,$\lambda = 5890 \ \mathring{A} = 5890 \times 10^{-10} \ m$,$c = 3 \times 10^8 \ m/s$.
$m = \frac{6.626 \times 10^{-34}}{5890 \times 10^{-10} \times 3 \times 10^8} = 3.75 \times 10^{-36} \ kg$.
The mass of an electron is $m_e = 9.11 \times 10^{-31} \ kg$.
Ratio $= \frac{m}{m_e} = \frac{3.75 \times 10^{-36}}{9.11 \times 10^{-31}} \approx 4.11 \times 10^{-6}$ times.