Define total internal reflection.

Total internal reflection occurs when the angle of incidence in the optically denser medium is greater than the critical angle, causing the light ray to be reflected in the denser medium, and no light ray being refracted.

Define critical angle.

Critical angle is the angle of incidence in the optically denser medium for which the angle of refraction in the less dense medium is 90o.

State the Laws of refraction.

First Law of Refraction:

The incident ray, the normal and the refracted ray all lie in the same plane.

Second Law of Refraction:

The ratio of sine of the angle of incidence to the sine of the angle of refraction is a constant.
(sin i / sin r = constant)