What should be the velocity of an electron so that its momentum becomes equal to that of a photon of wavelength $5200 \, \mathring{A}$? (Given: $h = 6.63 \times 10^{-34} \, J \cdot s$, $m_e = 9.1 \times 10^{-31} \, kg$)

What is the unit of energy in atomic and nuclear physics? Define it.

Two monochromatic beams $A$ and $B$ of equal intensity $I$ hit a screen. The number of photons hitting the screen by beam $A$ is twice that by beam $B$. What inference can you make about their frequencies?

The eye can detect $5 \times 10^4$ photons per square metre per second of green light $(\lambda = 5000 \ \mathring{A})$ while the ear can detect $10^{-13} \ W/m^2$. The factor by which the eye is more sensitive as a power detector than the ear is close to:

How is the intensity of radiation determined?

Monochromatic light of wavelength $667 \, nm$ is produced by a helium-neon laser. The power emitted is $9 \, mW$. The number of photons arriving per second on average at a target irradiated by this beam is: