Question

Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below.
Assertion (A): For monochromatic incident radiation, the emitted photoelectrons from a given metal have speed ranging from zero to a certain maximum value.
Reason (R): Each metal has a definite work function.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

Maximum kinetic energy of photoelectrons is given by \( K_{\text{max}} = h\nu - \phi \). The range in speed comes from electrons originating at different depths.

Answer 1

The Correct Option is B

In the photoelectric effect: - When monochromatic radiation is incident on a metal surface, the emitted photoelectrons can have kinetic energy ranging from 0 to a maximum value.
- This variation arises due to different depths of electrons within the metal. Surface electrons absorb energy more efficiently than deeper ones.
- Hence, Assertion (A) is true.
Now for the reason:
- Each metal has a definite work function \( \phi \), which is the minimum energy needed to liberate an electron from its surface.
- So, Reason (R) is also true.
However:
- The reason talks about the minimum energy required, not the range of speeds.
- The spread in speeds comes from variation in electron binding energies, not just the work function.
Thus, both statements are true, but the reason does not directly explain the assertion. Final answer: Option (B)