CBSE 2025, Compartment, Set 1

Question

Assertion (A): In process of photoelectric emission using a monochromatic light, all emitted electrons do not have the same kinetic energy.
Reason (R): If radiation falling on a photosensitive surface consists of different wavelengths, the energy of emitted photoelectrons by absorbing photons of different wavelengths, shall be different.

Select the correct option: 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.

Edvaya · Accepted Answer

The correct answer is Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).. **SOLUTION** **Assertion (A) is True:** Even when irradiated with highly controlled monochromatic light, electrons are emitted from varying depths within the metal. Electrons emitted from deeper layers undergo multiple internal collisions, losing portions of their kinetic energy before ejecting, meaning they emerge with a spread of kinetic energies (up to a specific $K_{max}$). **Reason (R) is True:** Incident radiation with multiple different wavelengths possesses multiple different photon energies, naturally causing a wide spread of emitted photoelectron energies. **Conclusion:** Although both are factually correct, Reason (R) explains polychromatic light, whereas Assertion (A) is explicitly about the internal collisions happening during monochromatic light. Thus, R is not the correct explanation for A.

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Physics > Modern Physics > Dual Nature Of Radiation And Matter

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