Concept:A photodiode detects light by converting incident photons into an electric current when operated in reverse bias.
Explanation:A photodiode is a
p-
n junction device designed for light detection.
It is connected in reverse bias so that normally only a very small dark current flows.
When light photons strike the junction, they generate electron-hole pairs in the depletion region.
These charge carriers increase the reverse current significantly.
The increase in reverse current is directly proportional to the intensity of the incident light.
Thus, by measuring this reverse current, we can accurately determine the light intensity.
In forward bias, the photodiode conducts heavily and cannot distinguish the light-generated current, so it is not used for detection.
An LED is used for emitting light, not for detecting it.
Answer:Therefore, the correct option is A: photodiode in reverse bias.