Question

In a p-n junction photocell, the value of the photo electromotive force produced by a monochromatic light depends upon-
$\left( {\text{A}} \right)$ The barrier voltage
$\left( {\text{B}} \right)$ The intensity of light falling on the cell
$\left( {\text{C}} \right)$ The frequency of the light falling on the cell
$\left( {\text{D}} \right)$ The voltage applied at the p-n junction

Answer 1

The answer is in the working of the photocell. Study the working of the photocell and try to derive a relationship between electromotive force and the quantities given in the options.

Complete step-by-step answer:
In a p-n junction photocell, the free electrons or the carriers move forward due to the light falling on it. The photons in the light, when they strike the free electrons, transmit the energy to the free electron and it moves forward, this develops a current and electromotive force in the photocell. The value of this electromotive force is dependent on the photons from the light. The more photons, higher will be the number of free electrons that will move. Hence the value depends on the intensity that is the number of photons of the light.
In simple words,
${\text{photo emf}} \propto {\text{current}}$
But, ${\text{current}} \propto {\text{intensity}}$
Thus, ${\text{photo emf}} \propto {\text{intensity}}$

Option B is the correct answer.

Note: Photocell was discovered in the year 1883, by an American scientist Charles Frits, it became mainstream in the late ${20^{th}}$ century. The most popular being the solar cell. The solar cell is used widely nowadays to produce electricity, there are also solar geysers, bulbs, emergency lights etc, solar cells are extremely useful for the countries with hot climate or sunny climate, and it is a non-conventional source of energy. It is non-polluting, cheap and environmentally friendly.
The p-n junction used in the photocell is a very widely used semiconductor diode, it allows current to flow only in one direction and hence it is used to convert alternating current to direct current. These devices are called rectifiers and are one of the basic applications of the p-n junction diodes.