The incident angle and the angle of refraction are not equal because light changes speed when it passes from one medium to another. Here's a breakdown:

* Snell's Law: This fundamental law of optics governs the relationship between the angles of incidence and refraction. It states:

* n1 * sin(θ1) = n2 * sin(θ2)

* Where:

* n1 is the refractive index of the first medium (where light is coming from)

* θ1 is the angle of incidence

* n2 is the refractive index of the second medium (where light enters)

* θ2 is the angle of refraction

* Refractive Index: The refractive index is a measure of how much a medium slows down light. Higher refractive index means light travels slower in that medium.

* Why the Angles Differ:

* When light travels from a medium with a lower refractive index (e.g., air) to a medium with a higher refractive index (e.g., water), it slows down.

* This change in speed causes the light path to bend towards the normal (an imaginary line perpendicular to the surface). This bending is the angle of refraction.

* Conversely, when light travels from a medium with a higher refractive index to a medium with a lower refractive index, it speeds up and bends away from the normal.

* Exception: When light travels between two media with the same refractive index, there is no change in speed, and the incident angle equals the angle of refraction (no bending).

In summary, the difference in the incident and refraction angles is due to the change in speed of light as it passes from one medium to another, dictated by the refractive indices of the two media.