Ligtht falls on a plane reflecting surface.For what angler of incidence is the reflected ray normal to the incident ray.

Options

A. `60^(@)`
B. `45^(@)`
C. `90^(@)`
D. `30^(@)`

Explanation

To solve the problem of finding the angle of incidence for which the reflected ray is normal to the incident ray, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Setup**:
- We have a plane reflecting surface.
- When light falls on this surface, it forms an angle of incidence (I) with the normal (a line perpendicular to the surface at the point of incidence).

2. **Define the Angles**:
- Let the angle of incidence be denoted as \( I \).
- The angle of reflection, according to the law of reflection, is equal to the angle of incidence, denoted as \( R \).

3. **Use the Law of Reflection**:
- According to the law of reflection, we have:
\[ I = R \]

4. **Relate the Angles**:
- The total angle formed between the incident ray and the reflected ray is:
\[ I + R = 90^\circ \]
- Since \( I = R \), we can substitute \( R \) with \( I \):
\[ I + I = 90^\circ \]
- This simplifies to:
\[ 2I = 90^\circ \]

5. **Solve for the Angle of Incidence**:
- Dividing both sides by 2 gives:
\[ I = \frac{90^\circ}{2} = 45^\circ \]

6. **Conclusion**:
- Therefore, the angle of incidence for which the reflected ray is normal to the incident ray is \( 45^\circ \).

### Final Answer:
- The angle of incidence is \( 45^\circ \).

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