For a light ray passing through a prism

Options

A. angle of deviation increases when angle of incidence is increased
B. angle of deviation decreases when angle of deviation is increased
C. When angle of incidence is increased or decreased from a particular value then in both cases angle of deviation increases.
D. Angle of deviation is approximately proportional to the refracting angle of prism provided prism is very thin.

Explanation

To solve the question regarding the behavior of a light ray passing through a prism, we will analyze the relationship between the angle of incidence and the angle of deviation.

### Step-by-Step Solution:

1. **Understanding the Prism**:
- A prism is a transparent optical element with flat, polished surfaces that refract light. The angle between the two plane surfaces of the prism is called the refracting angle (A).

2. **Angle of Incidence (i)**:
- The angle of incidence is the angle at which the incoming light ray strikes the surface of the prism.

3. **Angle of Deviation (D)**:
- The angle of deviation is the angle between the original path of the light ray and its path after passing through the prism.

4. **Behavior of Angle of Deviation**:
- When the angle of incidence increases from a small value, the angle of deviation initially decreases until it reaches a minimum value at a certain angle of incidence (let's call this angle i_min).
- Beyond this minimum angle of incidence, as the angle of incidence continues to increase, the angle of deviation starts to increase again.

5. **Analyzing the Options**:
- **Option A**: "The angle of deviation increases when the angle of incidence is increased."
- This is only true for the range after the minimum angle of incidence, so it is not universally correct.
- **Option B**: "The angle of deviation decreases when the angle of incidence is increased."
- This is also not universally correct as it only holds true until the minimum angle of incidence.
- **Option C**: "The angle of deviation increases when the angle of incidence is increased or decreased from a particular value."
- This option is correct because, after reaching the minimum angle, any increase or decrease from that angle will lead to an increase in the angle of deviation.
- **Option D**: "The angle of deviation is approximately proportional to the refracting angle of the prism."
- This is also correct, especially for thin prisms, as the angle of deviation can be expressed in terms of the refracting angle.

6. **Conclusion**:
- The correct options are C and D.