$A$ $100\,W$ light source is emitting radiation of wavelength $5000\,\mathring{A}$. The rate of emission of photons is of the order of:

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

The energy of a photon whose frequency is $10^{12} \text{ MHz}$ is:

An electron with rest mass $m_{0}$ moves with a speed of $0.8 c$. Its mass when it moves with this speed is

If $h$ is Planck's constant in $SI$ system,the momentum of a photon of wavelength $0.01 \, \mathring{A}$ is:

The ratio of the power of a light source $S_1$ to that of the light source $S_2$ is $2$. $S_1$ is emitting $2 \times 10^{15}$ photons per second at $600 \ nm$. If the wavelength of the source $S_2$ is $300 \ nm$,then the number of photons per second emitted by $S_2$ is . . . . . . $\times 10^{14}$.