Question

Assertion (A) : Photoelectric current depends upon the intensity of the incident radiation.
Reason (R) : Stopping potential is independent of the intensity of the incident radiation.

• 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:

For photoelectric effect questions, strictly memorize these two relationships: 1. Intensity governs the number of photons $\rightarrow$ affects Saturation Current. 2. Frequency governs photon energy $\rightarrow$ affects Maximum Kinetic Energy and Stopping Potential.

Answer 1

The Correct Option is B

Concept:
• In the photoelectric effect, the "intensity" of incident light is directly related to the number of photons striking the photosensitive surface per unit area per unit time.
• Provided the incident frequency is above the threshold frequency, each photon has a probability of ejecting exactly one electron.
• Therefore, increasing the intensity increases the number of emitted photoelectrons per second, which proportionally increases the photoelectric current.
• The "stopping potential" relates directly to the maximum kinetic energy of the emitted photoelectrons (\( eV_0 = K_{\text{max}} \)).
• According to Einstein's photoelectric equation (\( K_{\text{max}} = h\nu - \Phi \)), this maximum kinetic energy depends solely on the frequency of the incident light and the nature of the material, making it completely independent of intensity.

Step 1: Analyze the Assertion (A)
Assertion (A) states that photoelectric current depends on the intensity of the incident radiation. As established in the concepts, a higher intensity means a greater number of incident photons per second. More photons result in more photoelectrons being ejected per second, thereby increasing the photoelectric current. Thus, Assertion (A) is a true statement.

Step 2: Analyze the Reason (R) and its explanatory link
Reason (R) states that stopping potential is independent of the intensity of the incident radiation. Since intensity only affects the number of photons and not their individual energies, the maximum kinetic energy of the ejected electrons remains unchanged when intensity is varied. Consequently, the stopping potential required to halt these electrons also remains unchanged. Thus, Reason (R) is also a true statement. However, when determining if (R) explains (A), we see they describe two independent characteristics of the photoelectric effect. The independence of stopping potential from intensity does not serve as the logical cause or explanation for why photoelectric current relies on intensity.

Step 3: Conclusion
Both Assertion (A) and Reason (R) are experimentally true statements, but Reason (R) is not the correct explanation of Assertion (A). Therefore, option (B) is the correct choice.