Question

what do you understand by the deviation produced by prism ?why it is caused?

Answer 1

deviation produced by a prism means that a ray of light, on striking a prism, follows a different path.

this path is different from the oringinal path in which the incident ray struck the prism.

this is known as deviation.
Light is deflected as it enters a material with refractive index > 1. A ray of light is deflected twice in a prism. The sum of these deflections is thedeviation angle. When the entrance and exit angles are equal, the deviationangle of a ray passing through a prismwill be a minimum.

Answer 2

It means that a ray of light on striking a prism ,follows a different path.This path is different from the original one in which the incident ray struck the prism