The rest energy of an electron is

In an accelerator experiment on high-energy collisions of electrons with positrons,a certain event is interpreted as annihilation of an electron-positron pair of total energy $10.2 \; BeV$ into two $\gamma$-rays of equal energy. What is the wavelength associated with each $\gamma$-ray? $(1 \; BeV = 10^9 \; eV)$

An electron and a proton are detected in a cosmic ray experiment,the first with kinetic energy $10 \; keV$,and the second with $100 \; keV$. Which is faster,the electron or the proton? Obtain the ratio of their speeds. (Electron mass $= 9.11 \times 10^{-31} \; kg$,proton mass $= 1.67 \times 10^{-27} \; kg$,$1 \; eV = 1.60 \times 10^{-19} \; J$)

What is the energy and momentum of a photon having frequency $v$?

Let $n_r$ and $n_b$ be respectively the number of photons emitted by a red bulb and a blue bulb of equal power in a given time.

The energy of a photon with a wavelength of $6.20 \times 10^{-5} \ cm$ is ....... $eV$.