Introduction:
When a ray of light falls on a plane mirror, it undergoes reflection. The angle of incidence is the angle between the incident ray and the perpendicular to the mirror's surface, while the angle of reflection is the angle between the reflected ray and the perpendicular to the mirror's surface.

Explanation:
1. Angle of Incidence:
- The ray of light is incident on the plane mirror at an angle of 30 degrees. This means that the incident ray makes a 30-degree angle with the perpendicular to the mirror's surface.
- The perpendicular to the mirror's surface is a line drawn at a right angle to the mirror's surface at the point of incidence.

2. Angle of Reflection:
- According to the law of reflection, the angle of incidence is equal to the angle of reflection.
- This means that the reflected ray will make the same angle of 30 degrees with the perpendicular to the mirror's surface.

3. Explanation of the Law of Reflection:
- The law of reflection states that the angle of incidence is always equal to the angle of reflection.
- This law holds true for all types of surfaces, including plane mirrors.
- It can be explained using the principle that light travels in straight lines and that the angle at which it hits a surface determines the direction in which it is reflected.

Visual Representation:
To better understand the concept, consider the following visual representation:

```
Incident Ray Perpendicular Reflected Ray
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| | |
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| | |
| | |
| | |
-------|----------------------|---------------------- Mirror
| | |
| | |
| | |
| | |
| | |
| | |
```
In the given diagram, the incident ray makes an angle of 30 degrees with the perpendicular, and the reflected ray also makes an angle of 30 degrees with the perpendicular.

Conclusion:
When a ray of light is incident on a plane mirror at an angle of 30 degrees, the angle of reflection will also be 30 degrees. This is in accordance with the law of reflection, which states that the angle of incidence is equal to the angle of reflection.

60degree..as the incident ray make an 30 degree angle with plane so...it makes a 60 degree angle with normal...I think so..