A photon of energy `4 eV` is incident on a metal surface whose work function is `2 eV`. The minimum reverse potential to be applied for stopping the emission of electrons is

Options

A. 2V
B. 4V
C. 6V
D. 8V

Explanation

To solve the problem, we need to determine the minimum reverse potential (stopping potential) required to stop the emission of electrons when a photon of energy 4 eV is incident on a metal surface with a work function of 2 eV.

### Step-by-Step Solution:

1. **Understanding the Energy of the Photon**:
The energy of the incident photon is given as \( E_{photon} = 4 \, eV \).

2. **Understanding the Work Function**:
The work function of the metal is given as \( \phi = 2 \, eV \). The work function is the minimum energy required to remove an electron from the surface of the metal.

3. **Calculating the Kinetic Energy of Emitted Electrons**:
When the photon strikes the metal surface, if its energy is greater than the work function, electrons will be emitted. The kinetic energy (KE) of the emitted electrons can be calculated using the formula:
\[ KE = E_{photon} - \phi \]
Substituting the values:
\[ KE = 4 \, eV - 2 \, eV = 2 \, eV \]

4. **Relating Kinetic Energy to Stopping Potential**:
The stopping potential \( V_0 \) is related to the kinetic energy of the emitted electrons. The relationship is given by:
\[ KE = e \cdot V_0 \]
where \( e \) is the charge of an electron. Since we are working in electron volts, we can directly equate the kinetic energy to the stopping potential:
\[ 2 \, eV = e \cdot V_0 \]

5. **Calculating the Stopping Potential**:
From the equation above, we can solve for the stopping potential \( V_0 \):
\[ V_0 = \frac{KE}{e} = 2 \, eV \]

Thus, the minimum reverse potential required to stop the emission of electrons is **2 eV**.

### Final Answer:
The minimum reverse potential to be applied for stopping the emission of electrons is **2 eV**.