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 :

We need to evaluate the Assertion and Reason about the photoelectric effect.

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

This is TRUE. When a negative potential (called the stopping potential) is applied to the photoemissive surface, it repels the emitted electrons back. If the potential is sufficiently negative (equal to or greater than the stopping potential $$V_0$$), all photoelectrons are pushed back and the photocurrent becomes zero.

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."

This is TRUE. From Einstein's photoelectric equation:

$$eV_0 = h\nu - \phi$$

$$V_0 = \frac{h}{e}\nu - \frac{\phi}{e}$$

This shows that the stopping potential $$V_0$$ varies linearly with the frequency $$\nu$$ of incident radiation (with slope $$h/e$$ and y-intercept $$-\phi/e$$).

While both A and R are true, R explains the relationship between stopping potential and frequency. However, R does not directly explain why emission can be suppressed by a negative potential (which is explained by the work done by the electric field on the electrons). The reason behind A is that the electric field does negative work on electrons, not the linear relationship between $$V_0$$ and $$\nu$$.

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

The correct answer is Option (4): Both (A) and (R) are true but (R) is not the correct explanation of (A).