Q63 / 90 · JEE Main 2024 (04 Apr Shift 2) · Physics

Given below are two statements: one is labelled as Assertion $\mathbf{A}$ 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 $\mathbf{A}$ and $\mathbf{R}$ are correct and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$.
  • B
    Both $\mathbf{A}$ and $\mathbf{R}$ are correct and $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$.
  • Correct answer
    C
    $\mathbf{A}$ is not correct but $\mathbf{R}$ is correct.
  • D
    $\mathbf{A}$ is correct but $\mathbf{R}$ is not correct.

Solution

Intensity of light $\mathrm{I}=\frac{\mathrm{nh} \nu}{\mathrm{A}}$ Here $\mathrm{n}$ is no. of photons per unit time. $\mathrm{n}=\frac{\mathrm{IA}}{\mathrm{h} \nu}$ so on increasing frequency $v, \mathrm{n}$ decreases taking intensity constant. $\mathrm{k}_{\max }=\mathrm{h} v-\phi$
So on increasing $v$, kinetic energy increases.

Hence, the correct answer is option: 'C'.

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