Question

In a PN-junction photocell, the value of the photo electromotive force produced by monochromatic light is proportional to:
A) The intensity of the light falling on the cell
B) The frequency of the light falling on the cell
C) The voltage applied at the PN junction
D) The barrier voltage at the PN junction

Answer 1

Hint: The $PN$ junction photocell is also called a photodiode. The photodiode converts the photons into the current. This can also say that the photodiode produces current when the light falls on it. The electromotive force is similar to the potential difference across the two junctions. The electromotive force is developed inside the cell.

Complete step by step answer:
(i) The electromotive force is similar to the potential difference. According to Ohm’s law, a potential difference is directly proportional to the current and resistance. Hence the electromotive force is also proportional to the current.
(ii) The intensity of the light is defined as the power of the light incident in the unit area. We know that the power is directly proportional to current. And the current is proportional to the electromotive force. Therefore electromotive force is also proportional to the intensity of the light falling on the photocell.

Hence the correct option is A.

Additional information:
The interface or the boundary between the two-semiconductor material is known as a $PN$ junction. In the $PN$ junction the excess holes are found near the $p$ junction that is known as the positive side. The negative side or $n$ junction consists of the excess electrons.

Note:
The photodiodes are having many applications. As it transforms the light energy into the current, it is used in solar cells, LEDs, photodetectors, photoconductors, etc. It is also used as photosensors as it produces the current when photons fall on it. In medicine, it is used in Computed tomography (CT scan) and pulse oximeters.