Refraction is bending of light that occurs at interface between 2 media. The angle of refraction depends on the angle of incidence and the difference between the 2 media. When the incident ray is perpendicular to the surface, no refraction occurs and the ray passes straight through the second medium.
Bending light with a prism.
Not all wavelengths are refracted equally.
|Refraction is what gives rise to the shimmering bands of light often seen in the bottom of shallow pools of water.
Index of Refraction
The amount of bending of light depends not simply on the angle of the incident ray but also on the a property of the material called its index of refraction.
For the same angle of incidence the bending is greater for materials having higher indices of refraction.
When you view an object, O, submerged in an optical medium by looking along the normal through the surface, you see an image of the object at position I. The image is all that you see when looking through the interface – you are not looking directly at the object. Refraction causes the image to appear closer to you than the object. The index of refraction is defined as the ratio of the actual depth of the object to its apparent depth below the interface. In this figure, do represents the distance from the interface to the object and diis the distance from the interface to the image, i.e., the actual and apparent depths respectively.