A ray of light is incident on a plane mirror at an angle of `20^(@)` with the normal, at the point of incidence, Through what angle, the ray of light will be deviated from its direction of incidence ?

Options

A. `20^(@)`
B. `40^(@)`
C. `90^(@)`
D. `140^(@)`

Explanation

To solve the problem of how much a ray of light is deviated from its direction of incidence when it strikes a plane mirror at an angle of \(20^\circ\) with the normal, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Incident Ray**:
- The ray of light is incident on the plane mirror at an angle of \(20^\circ\) with respect to the normal.

2. **Apply the Law of Reflection**:
- According to the law of reflection, the angle of reflection is equal to the angle of incidence. Thus, the reflected ray will also make an angle of \(20^\circ\) with the normal.

3. **Visualize the Angles**:
- When the ray strikes the mirror, we can visualize the situation:
- The incident ray makes an angle of \(20^\circ\) with the normal.
- The reflected ray also makes an angle of \(20^\circ\) with the normal.

4. **Calculate the Angle of Deviation**:
- The angle of deviation (\(\theta\)) is defined as the angle between the direction of the incident ray and the direction of the reflected ray.
- The total angle formed between the incident ray and the reflected ray can be calculated as:
\[ \text{Total angle} = \text{Angle of incidence} + \text{Angle of reflection} = 20^\circ + 20^\circ = 40^\circ \]
- The angle of deviation is then given by:
\[ \theta = 180^\circ - \text{Total angle} = 180^\circ - 40^\circ = 140^\circ \]

5. **Final Answer**:
- Therefore, the angle through which the ray of light will be deviated from its direction of incidence is \(140^\circ\).