A light ray is incident normally on a plane mirror. The angle of reflection will be

Options

A. `120^@`
B. `90^@`
C. `45^@`
D. `0^@`

Explanation

To solve the question, "A light ray is incident normally on a plane mirror. The angle of reflection will be," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Setup**:
- A light ray is coming towards a plane mirror. When we say it is "incident normally," it means the light ray strikes the mirror at a 90-degree angle (perpendicular to the surface of the mirror).

2. **Identify the Normal Line**:
- The normal line is an imaginary line that is perpendicular to the surface of the mirror at the point of incidence. Since the light ray is incident normally, the normal line coincides with the direction of the incident ray.

3. **Apply the Law of Reflection**:
- According to the law of reflection, the angle of incidence (i) is equal to the angle of reflection (r). Mathematically, this is expressed as:
\[ \text{Angle of incidence (i)} = \text{Angle of reflection (r)} \]

4. **Determine the Angles**:
- Since the light ray is incident normally, the angle of incidence is 0 degrees (because it is perpendicular to the mirror). Therefore:
\[ i = 0^\circ \]

5. **Calculate the Angle of Reflection**:
- By the law of reflection:
\[ r = i = 0^\circ \]
- Thus, the angle of reflection is also 0 degrees.

6. **Conclusion**:
- Therefore, the angle of reflection when a light ray is incident normally on a plane mirror is **0 degrees**.

### Final Answer:
The angle of reflection will be **0 degrees**.

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