Question

The photocurrent in an experiment on photoelectric effect increases if:
A) The intensity of the source is increased.
B) The exposure time is increased
C) The intensity of the source is decreased
D) The exposure time is decreased

Answer 1

Hint: Photoelectric effect is the phenomenon of ejection of electrons (known as photoelectrons) from the surface of a metal when the light of suitable frequency is radiated on it.
It happens because photons in the light beam transfer their energy to the electrons on the metal surface allowing them to escape and flow under a potential difference, thus causing a photocurrent.

Complete step by step answer:
When the light of a suitable frequency (above the threshold frequency of the metal) is irradiated on the surface of a metal, the photons in the light beam collide with the electron on the surface and transfer a part of their energy to them. After gaining this energy, the electrons on the surface can escape the attractive forces from the metal. If made to flow under a potential difference, these electrons (or photoelectrons as they are now called), constitute an electric current known as photocurrent. This phenomenon is known as the photoelectric effect.
One important thing to note is that one photon interacts with only an electron. If the intensity of the light source is increased, more photons will be present in the light beam. Thus, more photons will interact with more electrons.
Thus, more photoelectrons can escape the metal surface. Since electric current is directly proportional to the amount of charge flowing, if more electrons flow, obviously a greater amount of charge will flow and thus the photocurrent will increase.

Hence, the correct answer is A) The intensity of the source is increased.

Note: The measure of photoelectric current does not depend on the time of exposure. Since one photon interacts with only one electron, it does not depend on how long the light exposure is kept on. The number of electrons ejected per second and thus essentially, the photocurrent will remain the same.
For the photoelectric effect to take place, the light must have a frequency equal to the threshold frequency of the metal. The threshold frequency is the minimum frequency of photon which on collision and complete energy transfer to an electron gives it the minimum required amount of energy to escape the surface of the metal.