Question

defin angular deviation.

Answer 1

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 the deviation angle. When the entrance and exit angles are equal, the deviation angle of a ray passing through a prism will be a minimum.

Answer 2

$\bold {ANSWER :-}$ The angle of deviation through a triangular prism is defined as the angle between the incident ray and the emerging ray.