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 junction diode.
In the light of the above statements, 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 the forward bias is more than the current in the reverse bias for a junction diode.
In the light of the above statements, choose the *correct* answer from the options given below:
- A.A is false but R is true
- B.A is true but R is false
- C.Both A and R are true but R is NOT the correct explanation of A
- D.Both A and R are true and R is the correct explanation of A
Show answer and solution
Correct option: C
Solution
Both statements are independently true but R does not explain A.
R is true: in a p-n junction, forward bias current is far larger than reverse bias current (due to the exponential I-V relationship).
A is true: in reverse bias, the minority carrier current (reverse saturation current) is small and very sensitive to light — each photon generates electron-hole pairs that add measurably to this small background current, giving a large fractional change and hence accurate light intensity measurement. In forward bias the large majority-carrier current swamps the photocurrent, making it hard to detect small changes due to light.
So R (forward bias > reverse bias current) is simply a general diode fact, not the reason photodiodes are used in reverse bias. The correct reason is the sensitivity and proportionality of photocurrent in reverse bias, making R not the correct explanation of A.
R is true: in a p-n junction, forward bias current is far larger than reverse bias current (due to the exponential I-V relationship).
A is true: in reverse bias, the minority carrier current (reverse saturation current) is small and very sensitive to light — each photon generates electron-hole pairs that add measurably to this small background current, giving a large fractional change and hence accurate light intensity measurement. In forward bias the large majority-carrier current swamps the photocurrent, making it hard to detect small changes due to light.
So R (forward bias > reverse bias current) is simply a general diode fact, not the reason photodiodes are used in reverse bias. The correct reason is the sensitivity and proportionality of photocurrent in reverse bias, making R not the correct explanation of A.
[JEE Main 2023 · 24 Jan · Shift 1 · Paper-1(B.E./B. Tech.)]