1. (a) Calculate the number of photons emitted per second by a 5 mW
laser assuming that it emits light of wavelength 6328 Å.[Ans: 1.6 ×
1016](b) The beam is allowed to fall normally on a plane mirror.
Calculate the force acting on the mirror.[Ans: 3.3 × 10 – 11 N] Get solution
2. Assume a 40 W sodium lamp (λ ≈ 5893Å) emitting light in all directions. Calculate the rate at which the photons cross an unit area placed normally to the beam at a distance at a distance of 10 m from the source.[Ans: ≈ 1017 photons/m2-sec] Get solution
3. In the photoelectric effect, a photon is completely absorbed by the electron. Show that the laws of conservation of energy and momentum cannot be satisfied simultaneously if a free electron is assumed to absorb the photon. (Thus the electron has to be bound to an atom and the atom undergoes a recoil when the electron is ejected. However, since the mass of the atom is much larger than that of the electron, the atom picks up only a small fraction of the energy, this is somewhat similar to the case of a tennis ball hitting a heavy object, the momentum of the ball is reversed with its energy remaining almost the same.) Get solution
4. If photoelectrons are emitted from a metal surface by using blue light, can you say for sure that photoelectric emission will take place with yellow light and with violet light? Get solution
2. Assume a 40 W sodium lamp (λ ≈ 5893Å) emitting light in all directions. Calculate the rate at which the photons cross an unit area placed normally to the beam at a distance at a distance of 10 m from the source.[Ans: ≈ 1017 photons/m2-sec] Get solution
3. In the photoelectric effect, a photon is completely absorbed by the electron. Show that the laws of conservation of energy and momentum cannot be satisfied simultaneously if a free electron is assumed to absorb the photon. (Thus the electron has to be bound to an atom and the atom undergoes a recoil when the electron is ejected. However, since the mass of the atom is much larger than that of the electron, the atom picks up only a small fraction of the energy, this is somewhat similar to the case of a tennis ball hitting a heavy object, the momentum of the ball is reversed with its energy remaining almost the same.) Get solution
4. If photoelectrons are emitted from a metal surface by using blue light, can you say for sure that photoelectric emission will take place with yellow light and with violet light? Get solution
