Optics in Physics : PYQs with Answers

Total internal reflection occurs when light passes from a denser to a rarer medium at an angle equal to or greater than the critical angle. It is the principle behind optical fibres.

When light travels from denser to rarer medium, the refracted ray bends away from the normal because speed increases. This follows Snell's law: $n_1 \sin\theta_1 = n_2 \sin\theta_2$.