The energy of a photon with a wavelength of $\lambda = 4000 \ \mathring{A}$ is equal to ... $eV$.

Which of the following has a mass closest in value to that of the positron? $(1\;a.m.u = 931\;MeV)$

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.

$A$ photon of wavelength $4400 \, \mathring{A}$ is passing through vacuum. The effective mass and momentum of the photon are respectively

The ratio of the energy of a photon with $\lambda = 150\,nm$ to that with $\lambda = 300\,nm$ is

The rest mass energy of an electron is $0.51 \ MeV$. If this electron is moving with a velocity of $0.8 \ c$ (where $c$ is the velocity of light in vacuum),then the kinetic energy of the electron is ........... $MeV$.