Observe the following diagrams and state the rules of refraction of light in different media using it.[Three diagrams: (a) a ray passing from a rarer medium (air) into a denser medium (glass) and bending towards the normal; (b) a ray passing from a d…

Answer: (a) Going into a denser medium the ray bends towards the normal, so r < i; (b) going into a rarer medium it bends away from the normal, so r > i; (c) at normal incidence the ray goes straight on, so i = r = 0.

(a) When light passes obliquely from a rarer medium (air) into a denser medium (glass or water), it slows down and bends towards the normal. The angle of refraction is smaller than the angle of incidence.

(b) When light passes obliquely from a denser medium into a rarer medium, it speeds up and bends away from the normal, so the angle of refraction is greater than the angle of incidence.

(c) When the incident ray is along the normal (angle of incidence 0º), it enters the second medium without any change in direction, so the angle of refraction is also 0º.

In every case the ratio \(\dfrac{\sin i}{\sin r}\) is a constant for the two media — Snell’s law — and this constant is the refractive index of the second medium with respect to the first.