Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Number of photons increases with increase in frequency of light.
Reason (R): Maximum kinetic energy of emitted electrons increases with the frequency of incident radiation.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both A and R are correct and R is NOT the correct explanation of A.
• B. A is correct but R is not correct.
• C. Both A and R are correct and R is the correct explanation of A.
• D. A is not correct but R is correct.

Answer 1

Answer: (D)

A is not correct but R is correct.

Answer 2

1. Analysis of Assertion A:
The intensity of light $I$ can be expressed as:
$I = \frac{nh\nu}{A},$ where $n$ is the number of photons per unit time, $h$ is Planck’s constant, $\nu$ is the frequency, and $A$ is the area. Rearranging for $n$:
$n = \frac{IA}{h\nu}.$ For a constant intensity $I$, if the frequency $\nu$ increases, the number of photons $n$ decreases. Thus, Assertion A is incorrect.

2. Analysis of Reason R:
According to the photoelectric effect, the maximum kinetic energy of emitted electrons is given by:
$K_{\text{max}} = h\nu - \phi,$ where $\phi$ is the work function of the material. As frequency $\nu$ increases, $K_{\text{max}}$ also increases. Therefore, Reason R is correct.

Thus, the correct answer is option (4): Assertion A is not correct, but Reason R is correct.