Mention two properties of a wave: one property which varies and the other which remains constant when the wave passes from one medium to another.

56 Express the refractive index of the medium. 57 If a ray of light passes from medium I to medium II without any change of direction, what can be said about the refractive indices of these media. 59 Name one factor on which the direction of bending of a ray of light depends. 60 A ray of light while traveling from a denser to a rarer medium, is incident at critical angle on the interface. What is the angle of refraction in the rarer medium?