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 electron 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 :

Solution

Physics sir · 5 steps

Both statements are true, but R tells you how much potential is needed, not why the potential works.

1. Check A. Make the emitter negative and the collector positive relative to it, and the field pushes ejected electrons back to the emitter. When the retarding potential reaches the stopping potential V₀, even the fastest electrons cannot get across, so the photocurrent falls to zero. A is true.
2. Check R. Einstein's equation sets the work done by the stopping potential equal to the maximum kinetic energy, eV₀ = hν - φ₀.

   V₀ = h/e ν - φ₀/e

3. Linear, so true. This is a straight line in ν with slope h/e. It does not pass through the origin, so V₀ is linear in ν but not proportional to it. R is true.
4. Does R explain A. A holds because a retarding field does negative work on the electrons and takes away their kinetic energy. R only says how the required V₀ changes with frequency. It would stay true if A were never mentioned, so it does not explain A.
5. So. Both (A) and (R) are true, but (R) is not the correct explanation of (A). The answer is (b).

The idea to keep. In assertion-reason questions, ask whether R gives the cause of A. A fact about how a quantity varies, like V₀ linear in ν, rarely explains why the effect happens at all.

Answer from the NTA final answer key. Solution by PrepWiser.