When a beam of light is incident on a plane mirror, it is found that a real image is formed. The incident beam must be

Options

A. Converging
B. Diverging
C. Parallel
D. Formation of real image by a plane mirror is impossible

Answer

To solve the question, we need to analyze the conditions under which a real image can be formed by a plane mirror.

### Step-by-Step Solution:

1. **Understanding Image Formation by Mirrors**:
- A plane mirror forms images based on the laws of reflection. The image formed is virtual and located behind the mirror, which means it cannot be projected onto a screen.

2. **Identifying Types of Light Beams**:
- The question provides four types of incident beams: converging, diverging, parallel, and states that the formation of a real image by a plane mirror is impossible.

3. **Analyzing Each Option**:
- **Converging Rays**:
- If a beam of converging rays (rays that come together at a point) strikes a plane mirror, the rays will reflect according to the laws of reflection. If these rays converge at a point before hitting the mirror, they can form a real image after reflection. Thus, this option is valid.

- **Diverging Rays**:
- Diverging rays (rays that spread apart) hitting a plane mirror will reflect and appear to come from a point behind the mirror. This results in a virtual image, not a real image. Therefore, this option is incorrect.

- **Parallel Rays**:
- Parallel rays striking a plane mirror will reflect off the mirror but will not converge or diverge. They will also not form a real image, making this option incorrect.

- **Formation of Real Image by Plane Mirror is Impossible**:
- This statement is false because a real image can be formed by converging rays, as established earlier.

4. **Conclusion**:
- The only type of incident beam that can lead to the formation of a real image by a plane mirror is a converging beam. Therefore, the correct answer is that the incident beam must be converging.

### Final Answer:
The incident beam must be **converging**.

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