Here's why:
Understanding the Concepts
* Refraction: When light travels from one medium to another (like air to water), it changes direction due to the difference in the speed of light in each medium. This bending of light is called refraction.
* Critical Angle: The critical angle is the angle of incidence at which the refracted ray travels along the boundary between the two media (at 90 degrees to the normal).
* Total Internal Reflection: If the angle of incidence exceeds the critical angle, the light is completely reflected back into the denser medium.
The Relationship
The angle between the reflected and refracted rays is 90 degrees *only* when the angle of incidence is equal to the critical angle. This is because:
1. When the angle of incidence is equal to the critical angle, the refracted ray travels along the boundary (at 90 degrees to the normal).
2. The reflected ray always makes the same angle with the normal as the incident ray.
3. Therefore, the reflected ray is also at 90 degrees to the refracted ray.
Why It's Not True in General
For angles of incidence less than the critical angle, the refracted ray will bend away from the normal, and the angle between the reflected and refracted rays will be less than 90 degrees.
Summary
The angle between reflected and refracted rays is 90 degrees only in the specific case where the angle of incidence is equal to the critical angle. For other angles of incidence, the relationship between these angles depends on Snell's Law, which governs the behavior of light during refraction.
