Question

According to physics, the movement of light from one medium to another in medium is denoted as refractive index..


But , we also know that light doesn't need any medium to travel !!!

Plz explain this __

Answer 1

 the speed of light is experimentally constant: independent of the movement of the source or detector or the direction in which it travels.We all know that Light is an EM wave (or kind of energy wave) but how does light travel especially when all other waves like sound need a medium to pass through? This is one of the great mysteries of physics.However we have some idea about light is able to travel through vacuum and air with ease.
I would not prefer to give theoretical answer here as many people have already given it. 
But if you try thinking about it intuitively the problem starts when you think of it as wave because wave needs a medium to travel.

Answer 2

Light need not need medium to travel but when the light does to denser medium it starts bending and It is called refraction