Question

What is saturation current in the photoelectric effect?

Answer 1

Hint: Photoelectric effect is a physical phenomenon in which electrically charged particles are released from the surface of a metal when it absorbs a certain threshold of electromagnetic radiation. This effect is often defined as the ejection of electrons from a metal plate when light/photons are incident on it.

Complete step by step solution:
The photoelectric effect occurs only if the light of a certain frequency that is more than the threshold frequency of the metal is incident on the surface of the metal. When the light of constant frequency and intensity more than the threshold frequency falls on an electrode (made up of metal) in a vacuum glass tube, the electrons near the surface and on the surface of the metal are ejected.

Suppose, for every photon incident on the metal surface, a single electron is ejected. Now, as the light is of constant intensity, the number of photons that are emitted and collide with the surface will be constant. Thus, the number of electrons that are emitted from the metal surface will also be constant.

Each electron that is ejected has a different amount of kinetic energy on the surface of the metal. Hence, not every ejected electron can successfully reach the collecting electrode. But, if the voltage is increased, more electrons can reach the other electrode. When the voltage is increased to a certain level, every electron that gets released is able to reach the other electrode, but as the number of electrons getting released is constant, the current becomes constant (saturation current) and no further increase in voltage will cause an increase in current. This occurrence is known as saturation current in the photoelectric effect.

Note: The photoelectric effect was discovered by the German physicist Heinrich Rudolf Hertz. In connection with his work on radio waves, Hertz observed that, when ultraviolet light is incident on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking takes place.