Question

Light of frequency two times the threshold frequency is incident on photosensitive material. If the incident frequency is made 1/3 rd and intensity is doubled, then the photoelectric current will

• A. increase
• B. decrease
• C. be zero
• D. be halved

Hint:

Photoelectric current depends on the intensity of light ONLY IF the incident frequency is above the threshold frequency. If $\nu < \nu_0$, the current is always zero, no matter how intense the light is.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We must determine the effect of changing incident light frequency and intensity on photoelectric current, specifically checking if the new frequency remains above the threshold for emission.

Step 2: Key Formula or Approach:
Photoelectric emission occurs only if the incident frequency $\nu \ge \nu_0$ (threshold frequency).

Step 3: Detailed Explanation:
1. Initially, the frequency $\nu = 2 \nu_0$. Since $2 \nu_0 > \nu_0$, photoelectric emission occurs.
2. The new frequency is given as $\nu' = \frac{1}{3} \nu = \frac{1}{3} (2 \nu_0) = \frac{2}{3} \nu_0$.
3. Since $\nu' = \frac{2}{3} \nu_0 < \nu_0$, the new frequency is below the threshold frequency required to eject electrons from the material.
4. Because the light frequency is below the threshold, no photoelectrons will be emitted, regardless of the increase in intensity. Therefore, the photoelectric current will be zero.

Step 4: Final Answer:
The photoelectric current will be zero, which corresponds to option (C).