Introduction

Accurate measurement of the refractive index of materials can be obtained using a prism made out of the material of interest. Rays passing though the prism deviate because of refraction. Simple ray (geometrical) optics and the use of Snell's law show that the index is directly related to the minimum angular deviation of a ray that passes through the prism at different angles of incidence. You can measure this minimum deviation directly for any ray that comprises a single wavelength of light (a monochromatic beam).

A cadmium lamp provides a few discrete wavelengths and for each wavelength the minimum deviation angle will be different. This is because the prism refractive index varies with wavelength (the property known as dispersion) and so you will also be able to measure this property as well.

There is an ISE where you can practice this experiment before your session. It can be found here.

Other Resources

• Prism Applet