* Refraction: When light passes from one medium to another (like from air to glass), it bends due to a change in speed. This bending is called refraction.
* Equal and Opposite Angles: When light enters the glass slab, it bends towards the normal (the perpendicular line to the surface). When it exits the slab, it bends away from the normal. Since the angles of incidence and emergence are equal, and the angles of refraction at each surface are also equal, the net effect is that the emergent ray is parallel to the incident ray.
* Parallel Surfaces: The rectangular shape of the slab ensures that the two surfaces through which the light enters and exits are parallel to each other. This parallelism plays a key role in the equal angles of incidence and emergence.
Here's a detailed explanation:
1. Incident Ray: Light enters the glass slab at an angle.
2. First Refraction: Light bends towards the normal as it enters the denser medium (glass).
3. Second Refraction: Light bends away from the normal as it exits the glass and returns to the less dense medium (air).
4. Parallelism: Due to the parallel surfaces of the slab, the angle at which the light exits the glass is the same as the angle at which it entered.
5. Emergent Ray: Consequently, the emergent ray is parallel to the incident ray.
Important Note: The emergent ray is only parallel to the incident ray if the glass slab has parallel surfaces. If the surfaces are not parallel, the emergent ray will not be parallel to the incident ray.
