Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Photodiodes are preferably operated in reverse bias condition for light intensity measurement.
Reason R: The current in the forward bias is more than the current in the reverse bias for a $$p - n$$ junction diode.
In the light of the above statement, choose the correct answer from the options given below :

Assertion A: Photodiodes are preferably operated in reverse bias condition for light intensity measurement.

Reason R: The current in forward bias is more than the current in reverse bias for a p-n junction diode.

Evaluation of Assertion A:

In reverse bias, a photodiode has a very small dark current. When light falls on it, the photogenerated carriers (electron-hole pairs) contribute to a current that is directly proportional to the light intensity. This makes the change in current due to light easily measurable. In forward bias, the large forward current would overwhelm the photocurrent, making measurement difficult. Assertion A is true.

Evaluation of Reason R:

In a p-n junction diode, forward bias current is indeed much larger than reverse bias current (reverse bias gives only a small leakage current). Reason R is true.

Does R explain A?

The reason photodiodes are used in reverse bias is specifically because the small reverse current makes it easier to detect light-induced changes. While R states a true fact about diode currents, it does not directly explain why reverse bias is preferred for light measurement (it does not mention photocurrent sensitivity or signal-to-noise ratio). So R is not the correct explanation of A.

Both A and R are true but R is NOT the correct explanation of A. The answer is Option 2.