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Electronic Devices question

2023 · 24 Jan · Shift 1 · Q45
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Electronic Devices question

2023 · 24 Jan · Shift 1 · Q45

JEE MainPhysicsElectronic DevicesMCQ+4 / −1
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−np-np−n junction diode. In the light of the above statements, choose the correct answer from the options given below :
  1. A
    Both A and R are true and R is the correct explanation of A
  2. B
    A is false but R is true
  3. C
    A is true but R is false
  4. D
    Both A and R are true but R is NOT the correct explanation of A
View written solutionFree

Correct answer: D

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

    This statement is true.

    • A photodiode is usually used in reverse bias because under reverse bias, the current due to incident light (photocurrent) becomes significant and varies almost linearly with light intensity.
    • Reverse bias also improves response speed and sensitivity for detection purposes.

  2. Reason R: The current in the forward bias is more than the current in the reverse bias for a ppp-nnn junction diode.

    This statement is also true.

    • In a normal ppp-nnn junction diode, forward bias allows large current to flow.
    • In reverse bias, only a small reverse saturation current flows (until breakdown).

  3. Check whether R explains A:

    • Although R is true, it is not the correct explanation for why photodiodes are operated in reverse bias.
    • The real reason is that in reverse bias, the photocurrent is more directly measurable and depends on light intensity.
    • If operated in forward bias, the large forward current would mask the photocurrent, making light detection less effective.

  4. Conclusion:

    • Both A and R are true.
    • But R is not the correct explanation of A.

Therefore, the correct option is:

D\boxed{D}D​

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