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 strikes a metal, emitted photoelectrons exhibit a kinetic energy spectrum from zero up to a maximum. - This energy variation is attributed to electrons originating from different depths within the metal, with surface electrons absorbing energy more effectively than those deeper within. - Therefore, Assertion (A) is validated. Regarding the reason: - Every metal possesses a characteristic work function (\( \phi \)), representing the minimum energy required to eject an electron from its surface. - Consequently, Reason (R) is also substantiated. However: - The reason addresses the threshold energy for electron liberation, not the distribution of kinetic energies or speeds. - The observed spread in kinetic energies arises from variations in electron binding energies, beyond just the work function. In conclusion, while both statements are factually correct, the provided reason does not fully account for or directly explain the assertion regarding the range of photoelectron kinetic energies. Final answer: Option (B)