The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4eV. The stopping potential in volt is
(a)2 (b) 4 (c ) 6 (d) 10

Explanation

To find the stopping potential when photons of energy 6 eV fall on a surface and the maximum kinetic energy of the emitted photoelectrons is 4 eV, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Photoelectric Effect**:
The photoelectric effect states that when light (photons) hits a surface, it can eject electrons. The energy of the incoming photons is used to overcome the work function of the material and provide kinetic energy to the emitted electrons.

2. **Given Data**:
- Energy of the incoming photons (E_photon) = 6 eV
- Maximum kinetic energy of emitted photoelectrons (K_max) = 4 eV

3. **Using the Photoelectric Equation**:
The relationship between the energy of the incoming photons, the work function (φ), and the maximum kinetic energy of the emitted electrons is given by:
\[ E_{\text{photon}} = \phi + K_{\text{max}} \]
Rearranging this gives:
\[ \phi = E_{\text{photon}} - K_{\text{max}} \]

4. **Calculating the Work Function (φ)**:
Substituting the known values into the equation:
\[ \phi = 6 \, \text{eV} - 4 \, \text{eV} = 2 \, \text{eV} \]

5. **Finding the Stopping Potential (V₀)**:
The stopping potential is related to the maximum kinetic energy of the emitted electrons by the equation:
\[ V_0 = \frac{K_{\text{max}}}{e} \]
Since we are working in electron volts, we can directly use the kinetic energy in eV as the stopping potential in volts:
\[ V_0 = K_{\text{max}} = 4 \, \text{V} \]

6. **Conclusion**:
The stopping potential is 4 volts.

### Final Answer:
The stopping potential in volts is **4** (option b).

---