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JEE Main 2025 Jan 29 Shift 1, Physics Q11: Introduction and Photoelectric Effect

JEE Main2025Jan 29, Shift 1Physics
Q.

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : Emission of electrons in photoelectric effect can be suppressed by applying a sufficiently negative electric potential to the photoemissive substance.

Reason (R) : A negative electric potential, which stops the emission of electrons from the surface of a photoemissive substance, varies linearly with frequency of incident radiation.

In the light of the above statements, choose the most appropriate answer from the options given below:

  1. A

    (A) is false but (R) is true.

  2. B

    (A) is true but (R) is false.

  3. C

    Both (A) and (R) are true and (R) is the correct explanation of (A).

  4. D

    Both (A) and (R) are true but (R) is not the correct explanation of (A).

Solution

Applying a sufficiently negative potential to the emitter (or equivalently a positive stopping potential at the collector) raises the energy barrier so that even the most energetic photoelectrons can no longer reach the anode. Assertion is true.

The Einstein photoelectric equation gives , i.e. the stopping potential is a linear function of frequency Reason is also true.

However, Reason simply states a property of versus . It does not explain why applying a negative potential suppresses emission, it only quantifies how the threshold depends on Hence Reason is not the correct explanation of Assertion.

Concept behind this question

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