Proving Parallelism of Incident and Emergent Rays
To prove that the incident ray is parallel to the emergent ray, we can use the principle of refraction at the interface of two different mediums.

Key Steps:
1. Assumption: Let's assume that the incident ray enters the first medium and strikes the interface at a certain angle of incidence.
2. Refraction: According to the laws of refraction, the incident ray will bend towards or away from the normal depending on the refractive indices of the two mediums.
3. Parallel Emergent Ray: If the angle of incidence is such that the emergent ray in the second medium is parallel to the incident ray in the first medium, then we can conclude that the incident ray is parallel to the emergent ray.
4. Proof: To prove this, we can use the Snell's Law which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. If this ratio is found to be 1, then the incident and emergent rays are parallel.
5. Observation: By observing the direction of the emergent ray and comparing it with the incident ray, we can determine if they are indeed parallel.
By following these steps and principles of refraction, we can prove that the incident ray is parallel to the emergent ray when light passes through different mediums.

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