When light source is placed at 1 m distant from photo electric cell , then value of stopping potential is obtained 4 volt. If it is placed at 4 m distant, then value of stopping potential becomes -

Options

A. 2 volt
B. 1 volt
C. 4 volt
D. 16 volt

Answer

To solve the problem regarding the stopping potential when the light source is moved from 1 meter to 4 meters away from the photoelectric cell, we can follow these steps:

### Step 1: Understand the Concept of Stopping Potential
The stopping potential (V₀) is the negative potential that must be applied to the anode to stop the most energetic photoelectrons emitted from the cathode. It is related to the maximum kinetic energy (KE) of the emitted electrons, which is given by the equation:
\[ KE = eV₀ \]
where \( e \) is the charge of the electron.

### Step 2: Analyze the Given Information
From the problem, we know:
- When the light source is at 1 meter, the stopping potential is 4 volts.
- We need to find the stopping potential when the light source is moved to 4 meters.

### Step 3: Consider the Effect of Distance on Light Intensity and Frequency
When the distance of the light source from the photoelectric cell is increased, the intensity of the light reaching the cell decreases due to the inverse square law. However, the frequency of the light remains unchanged since we are using the same light source.

### Step 4: Relate Stopping Potential to Frequency
The stopping potential depends on the frequency of the incident light, not on its intensity. Since the frequency of the light does not change when moving the source from 1 meter to 4 meters, the energy of the emitted photoelectrons remains the same.

### Step 5: Conclude the Stopping Potential
Since the frequency remains the same, the maximum kinetic energy of the emitted electrons remains unchanged. Therefore, the stopping potential will also remain unchanged.

Thus, the stopping potential when the light source is placed at 4 meters will still be:
\[ V₀ = 4 \text{ volts} \]

### Final Answer
The stopping potential when the light source is placed at 4 meters distance is **4 volts**.

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