Question

When monochromatic radiation of intensity $I$ falls on a metal surface, the number of photoelectrons and their maximum kinetic are $N$ and $T$ respectively. If the intensity of radiation is $2I$, the number of emitted electrons and their maximum kinetic energy are respectively:
A) N and 2T
B) 2N and T
C) 2N and 2T
D) N and T

Answer 1

Hint: The photoelectric effect is associated with the particle nature of light. The intensity of the radiation will affect the number of electrons selected but will not affect the maximum kinetic energy of the electrons.

Complete step by step answer:
In the photoelectric effect, when photons that have energy above a certain threshold, interact with a metal, they eject electrons from the metal surface which is measured in the form of an electric current.
The photoelectric work function is the threshold energy required by the radiation or photons that are incident on the surface of the metal. We can use the term radiation interchangeably with photons in this case.
The incoming radiation must have energy higher than the threshold work function to cause the photoelectric effect. This can be written as that the frequency of the incoming radiation must be higher than the threshold frequency of the metal to cause the photoelectric effect.
Above the threshold frequency, when the intensity of the radiation is doubled, only the number of electrons that are ejected will be doubled. But the maximum kinetic energy of the electrons will remain unaffected.
Hence the new number of electrons will be $2N$ and the maximum kinetic energy will be $T$.

So, option (B) is correct.

Note: The maximum kinetic energy of the electrons will only be affected by a change in the incoming radiation frequency. Since the incoming radiation frequency is not changed, the maximum kinetic energy will also not change.