Question

Can someone explain why can we use material with high indices of refraction to focus light?

Answer 1

The amount of bent of light depend on the refractive index of the medium.  Refractive index a measure of how light propagates through a material. The higher the refractive index the slower the light travels, results a correspondingly increased change in the direction of the light within the material. More index, more will be bent to the normal and can be focused on one point. For example in case of convex lens, middle part is made more thick , more refractive index, so that it focus all tha parallel light on the focal point. More refractive index slows down the light by changing the direction and can be focused to desired point by increasing the refractive index.