Refractive Index: IGCSE Physics Definition

In IGCSE Physics, the refractive index, n, for the ratio of angles, is defined as the ratio of the sine of the angle of incidence and the sine of the angle of refraction of a wave in two different regions.

The refractive index for the ratio of angles is given by the equation:

Where:

• = the refractive index of the material

• = angle of incidence of the light ()

• = angle of refraction of the light ()

The refractive index, n, for the ratio of speeds, is defined as the ratio of the speeds of a wave in two different regions. It is given by the equation:

The refractive index is a number that is always larger than 1 and is different for different materials. Objects which are more optically dense have a higher refractive index, e.g. n is about 2.4 for diamond. Objects which are less optically dense have a lower refractive index, e.g. n is about 1.5 for glass. Since the refractive index is a ratio, it has no units.

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