A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (∠ i). He then measures the corresponding values of the angle of refraction (∠ r) and the angle of emergence (∠ e) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be

When a ray of light enters a rectangular glass slab from air (an optically rarer medium) to glass (an optically denser medium), it bends towards the normal. Therefore, the angle of refraction ($\angle r$) is less than the angle of incidence ($\angle i$), i.e., $\angle i > \angle r$.

When the light ray emerges from the opposite parallel face of the glass slab into the air, it bends away from the normal. Since the two refracting surfaces of the slab are parallel, the extent of bending of the ray of light at the opposite faces is equal and opposite. Thus, the emergent ray is parallel to the incident ray, which means the angle of emergence ($\angle e$) is equal to the angle of incidence ($\angle i$), i.e., $\angle i = \angle e$.

Combining these two relations, we get:

$$\angle i = \angle e > \angle r$$

Hence, Option B is correct.

• Option A is incorrect because $\angle r$ is not greater than $\angle e$.
• Option C is incorrect because $\angle i$ is greater than $\angle r$, not less.
• Option D is incorrect because $\angle r$ is smaller than $\angle i$ and $\angle e$, not greater.