For refractin of light through a prism

Options

A. a. For every angle of deviation there are two angles of incidence.
B. b. The light travelling inside an isosceles prism is necessarilly parallel to the base when prism is set for minimum deviation.
C. c. There are two angles of incidence for maximum deviation.
D. d. Angle of minimum deviation will increase if refrative index of prism is increased keeping the outside medium unchanged.

Explanation

To analyze the refraction of light through a prism and determine the correctness of the statements provided, we will go through each statement step by step.

### Step-by-Step Solution:

1. **Statement A**: "For every angle of deviation, there are two angles of incidence."
- **Analysis**: When light passes through a prism, for most angles of deviation, there are indeed two angles of incidence that can produce the same angle of deviation. However, at the angle of minimum deviation (Δ_min), there is only one unique angle of incidence (I). Therefore, this statement is **incorrect**.

2. **Statement B**: "The light traveling through an isosceles prism is necessarily parallel to the base when the prism is set for minimum deviation."
- **Analysis**: At minimum deviation, the light ray entering and exiting the prism is symmetrically aligned. In an isosceles prism, the angles of incidence and refraction are equal (r1 = r2), and the light ray is indeed parallel to the base of the prism. Thus, this statement is **correct**.

3. **Statement C**: "There are two angles of incidence for maximum deviation."
- **Analysis**: Maximum deviation occurs when the angle of incidence is either 90 degrees (the ray is parallel to the base) or when the angle of refraction at the second face is 90 degrees (the ray emerges parallel to the base). Therefore, there are indeed two angles of incidence that can yield maximum deviation. This statement is **correct**.

4. **Statement D**: "The angle of minimum deviation will be increased if the refractive index of the prism is increased, keeping the outside medium unchanged."
- **Analysis**: The formula for the angle of deviation (Δ) is given by Δ = A(μ - 1), where A is the angle of the prism and μ is the refractive index. If the refractive index (μ) increases while keeping A constant, the angle of minimum deviation (Δ_min) will also increase. Thus, this statement is **correct**.

### Conclusion:
- **Correct Statements**: B, C, and D are correct. Statement A is incorrect.