Question

What condition is required to detect the light?
A. The photodiode has to be forward biased
B. The photodiode has to be reverse biased
C. The LED has to be connected in forward bias mode
D. The LED has to be connected in reverse bias mode

Answer 1

Photodiode is a device which is used to detect light. In the condition of reverse bias, more incident photons are converted to electric current and in forward bias condition, less incident photons get changed to electric current.

Complete step-by-step solution :The device which is used to detect light is called Photodiode. This device is a PN junction which generates current when light falls on it. The other names for this device are photodetector and photosensor.
This device works in reverse biased condition and changes light energy to electrical energy.
This device operates on the principle of Photoelectric effect. This device responds quickly when shown to light and its cost is also low but this depends upon temperature.
They are often found in counters, switching circuits and are also used in alarm systems.
In forward bias condition, the depletion’s width decreases because the applied forward bias voltage decreases in the diode. Therefore, less amount of incident photons changes to electric current by which the efficiency gets low.
In reverse bias condition, the depletion’s width increases because the applied reverse bias voltage increases in the diode. So, when we apply more voltage, more incident photons convert to electric current which increase its efficiency.
Therefore, photodiode is used in reverse biased condition due to higher efficiency.
So, option (B) is correct.

Note:-
There is higher efficiency in reverse biased conditions in photodiodes due to more electric current. Photodiode is the device which uses photoelectric effect to detect light.