In a Young's double slit experiment a monochromatic laser beam is used to provide the coherent source. To emit the monochromatic laser beam electron has to jump through an energy band of energy difference $4.2eV$ inside the laser. The wavelength of the laser beam emitted by the laser source is ___ $\dot{A}$.

Q. Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW.
Find the energy and momentum of each photon in the light beam,

Q. A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances.The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth ?

Q. Monochromatic light of frequency $6\times {10}^{14}$ Hz is produced by a laser. The power emitted is $2\times {10}^{-3}$ W
(i) What is the energy of the photon in the light beam?
(ii) How many photons per second, on an average are emitted by the source ?

Q. A) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium-neon laser. The power emitted is $9.42\text{mW}$ .Find the energy and momentum of each photon in the light beam.

B) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium-neon laser. The power emitted is $9.42\text{mW}$. How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area).

C) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium − neon laser. The power emitted is $9.42\text{mW}$. How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?"

Q. A 5.0 W laser emits monochromatic light of frequency 8.0 $\times {10}^{14}Hz$. The number of photons emitted per second by the laser is