The angle of incident of a light rays incidents on the surface of a plane mirror is `30^@` . The angle of deviation is

Options

A. `120^@`
B. `30^@ `
C. `60^@`
D. `90^@`

Explanation

To find the angle of deviation when a light ray strikes a plane mirror at an angle of incidence of \(30^\circ\), we can follow these steps:

### Step 1: Understand the setup
- A plane mirror reflects light. When a light ray strikes the mirror, it creates an angle of incidence with the normal (an imaginary line perpendicular to the surface of the mirror).

### Step 2: Identify the angle of incidence
- The angle of incidence (\(i\)) is given as \(30^\circ\).

### Step 3: Apply the law of reflection
- According to the law of reflection, the angle of reflection (\(r\)) is equal to the angle of incidence. Therefore, \(r = i = 30^\circ\).

### Step 4: Determine the angle of deviation
- The angle of deviation (\(D\)) is defined as the angle between the direction of the incident ray and the direction of the reflected ray.
- The total deviation can be calculated using the formula:
\[ D = i + r \]
- Substituting the values:
\[ D = 30^\circ + 30^\circ = 60^\circ \]

### Step 5: Calculate the angle of deviation
- However, we need to find the angle of deviation from the original path of the incident ray to the final path of the reflected ray. The deviation angle is actually calculated as:
\[ D = 180^\circ - (i + r) \]
- Therefore:
\[ D = 180^\circ - 60^\circ = 120^\circ \]

### Conclusion
- The angle of deviation is \(120^\circ\).