Write the equation for the effective mass of a photon.

(N/A) According to Einstein's mass-energy equivalence,the energy $E$ of a photon is given by $E = mc^2$,where $m$ is the effective mass and $c$ is the speed of light.
Also,the energy of a photon is given by $E = h\nu = \frac{hc}{\lambda}$,where $h$ is Planck's constant,$\nu$ is the frequency,and $\lambda$ is the wavelength.
Equating the two expressions for energy: $mc^2 = \frac{hc}{\lambda}$.
Solving for $m$,we get the effective mass of the photon: $m = \frac{h}{c\lambda} = \frac{h\nu}{c^2}$.