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MCQEasyJEE 2023LED, Photodiode & Solar Cell

JEE Physics 2023 Question with Solution

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\text{-}n 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

    Both A and R are true but R is NOT the correct explanation of A

  • C

    A is true but R is false

  • D

    Both A and R are true and R is the correct explanation of A

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Assertion A says that photodiodes are preferably operated in reverse bias for light intensity measurement. Reason R says that forward bias current is more than reverse bias current for a p-np\text{-}n junction diode.

Find: Which option correctly describes the truth of A and R, and whether R explains A.

Photodiodes are operated in reverse bias because the fractional change in current due to light is easier to detect in reverse bias.

It is true that the current in forward bias is greater than the current in reverse bias for a p-np\text{-}n junction diode.

However, that fact does not explain why photodiodes are used in reverse bias for measurement.

Therefore, A is true and R is also true, but R is not the correct explanation of A.

The correct option is B.

Common mistakes

  • Assuming that any true reason automatically explains the assertion. Here R is true, but it does not explain the operating choice of photodiodes. Check causal connection, not only truth value.

  • Confusing ordinary diode conduction with photodiode detection. A photodiode is used in reverse bias because light-induced current changes are easier to measure there, not because reverse current is larger.

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