Einstein's photoelectric equation is `E_k = hv - phi` . In this equation `E_k` refers to

Options

A. kinetic energy of all the emitted electrons
B. mean kinetic energy of emitted electrons
C. maximum kinetic energy of emitted electrons
D. minimum kinetic energy of emitted electrons

Explanation

To solve the question regarding Einstein's photoelectric equation \(E_k = hv - \phi\), we need to analyze what each term in the equation represents, particularly focusing on \(E_k\).

### Step-by-Step Solution:

1. **Understanding the Equation**:
The equation \(E_k = hv - \phi\) is derived from Einstein's explanation of the photoelectric effect. Here, \(E_k\) represents the kinetic energy of the emitted electrons.

2. **Identifying the Terms**:
- \(hv\): This term represents the energy of the incident photon, where \(h\) is Planck's constant and \(v\) (or \(\nu\)) is the frequency of the incident light.
- \(\phi\): This is known as the work function of the material, which is the minimum energy required to remove an electron from the surface of the metal.

3. **Kinetic Energy Calculation**:
When a photon strikes the surface of a metal, it can transfer its energy to an electron. If the energy of the photon (\(hv\)) is greater than the work function (\(\phi\)), the excess energy is converted into the kinetic energy of the electron. Therefore, the kinetic energy \(E_k\) of the emitted electron is given by the difference between the energy of the photon and the work function.

4. **Conclusion**:
From the equation, we can conclude that \(E_k\) refers to the maximum kinetic energy of the emitted electrons after overcoming the work function barrier.

### Final Answer:
In Einstein's photoelectric equation \(E_k = hv - \phi\), \(E_k\) refers to the **maximum kinetic energy of the emitted electrons**.

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