A ray of light is incident normally on a plane glass slab. What will be (i) the angle of refraction, and (ii) the angle of deviation for the ray ?

Answer

To solve the problem, we need to analyze the situation where a ray of light is incident normally on a plane glass slab.

### Step-by-Step Solution:

1. **Identify the Angle of Incidence**:
- When a ray of light is incident normally on a surface, the angle of incidence (i) is 0 degrees. This is because "normally" means that the ray hits the surface at a right angle (perpendicular).

2. **Apply Snell's Law**:
- Snell's Law states that \( \frac{\sin i}{\sin r} = \frac{n_1}{n_2} \), where:
- \( n_1 \) is the refractive index of the first medium (air, approximately 1).
- \( n_2 \) is the refractive index of the second medium (glass, typically around 1.5).
- Since \( i = 0 \), we have \( \sin i = \sin 0 = 0 \).

3. **Calculate the Angle of Refraction**:
- Substituting into Snell's Law:
\[ \sin r = \frac{n_2}{n_1} \times \sin i = \frac{1.5}{1} \times 0 = 0 \]
- Therefore, \( \sin r = 0 \) implies that \( r = 0 \) degrees.
- Thus, the angle of refraction (r) is also 0 degrees.

4. **Determine the Angle of Deviation**:
- The angle of deviation (D) is defined as the angle between the incident ray and the emergent ray after passing through the medium.
- Since both the angle of incidence and angle of refraction are 0 degrees, the ray does not deviate from its original path.
- Therefore, the angle of deviation (D) is also 0 degrees.

### Final Answers:
- (i) The angle of refraction is 0 degrees.
- (ii) The angle of deviation is 0 degrees.