Index of Refraction

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.

Refraction occurs at the interface between air and water. Moreover, the amount of refraction varies due to small undulations at the water’s surface, thus causing light to be concentrated in different amounts at the bottom of the pool.

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, d_o represents the distance from the interface to the object and d_iis the distance from the interface to the image, i.e., the actual and apparent depths respectively.

Indices of refraction for some materials found in the nature are listed in the table to the right.