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 regarding the nature of the incident beam of light on a plane mirror that results in a real image, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Formation of Images by a Plane Mirror**:
- A plane mirror always forms a virtual image. This is because the light rays reflecting off the mirror appear to diverge from a point behind the mirror, making the image virtual and upright.

2. **Analyzing the Given Information**:
- The question states that a real image is formed when light is incident on a plane mirror. This is unusual because, under normal circumstances, a plane mirror does not produce real images.

3. **Considering the Options**:
- The options provided are:
a) Converging
b) Diverging
c) Parallel
d) Formation of a real image by the plane mirror is not possible

4. **Evaluating Each Option**:
- **Option d**: "Formation of a real image by the plane mirror is not possible" – This option is correct because a plane mirror cannot form a real image.
- **Option a**: "Converging" – If the incident beam were converging, it would mean that the light rays are coming together at a point before reflecting off the mirror. However, this would not lead to a real image.
- **Option b**: "Diverging" – A diverging beam would spread out, and similarly, would not form a real image.
- **Option c**: "Parallel" – A parallel beam would reflect back parallel to itself, which also does not lead to a real image.

5. **Conclusion**:
- Since a plane mirror cannot form a real image, the correct answer is that the formation of a real image by the plane mirror is not possible.

### Final Answer:
The incident beam must be such that the formation of a real image by the plane mirror is not possible.