If the angle between incident ray and reflected ray is `120^@`, what is the angle of incidence ?

Options

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

Explanation

To find the angle of incidence when the angle between the incident ray and the reflected ray is given as 120 degrees, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Problem**: We are given that the angle between the incident ray and the reflected ray is 120 degrees. We need to find the angle of incidence.

2. **Identify the Relationship**: According to the laws of reflection, the angle of incidence (i) is equal to the angle of reflection (r). This can be expressed as:
\[ i = r \]

3. **Express the Angle Between Rays**: The angle between the incident ray and the reflected ray can be expressed in terms of the angle of incidence and the angle of reflection:
\[ \text{Angle between incident ray and reflected ray} = i + r \]
Since \(i = r\), we can rewrite this as:
\[ \text{Angle between incident ray and reflected ray} = i + i = 2i \]

4. **Set Up the Equation**: We know from the problem that the angle between the incident ray and reflected ray is 120 degrees. Therefore, we can set up the equation:
\[ 2i = 120^\circ \]

5. **Solve for the Angle of Incidence**: To find the angle of incidence (i), we divide both sides of the equation by 2:
\[ i = \frac{120^\circ}{2} = 60^\circ \]

6. **Conclusion**: The angle of incidence is 60 degrees.

### Final Answer:
The angle of incidence is \(60^\circ\).

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