Express the refractive index of the medium.

54 With the help of a labeled ray diagram show the formation of image of an object by a compound microscope. 55 What is meant by refraction? 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. 58 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.