Prism Spectrometer

The refractive index is one of the basic descriptors of materials that we use for their optical properties. It governs the design of lenses and other optical components, such as photonic devices in fibre optic communication systems. By studying a prism made from the material of interest, you can accurately measure the refractive index. 

Rays passing through the prism deviate because of refraction. Simply ray (geometrical) optics and the use of Snell’s law shows that the index is directly related to the minimum angular deviation of a ray that passes through the prism at different angles of incidence. 

In this experiment, you will use a spectrometer to measure the minimum deviation angle of light passing through a prism and use that to calculate the refractive index. A cadmium lamp provides a few discrete wavelengths; 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”), so this property can be measured as well. 

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

Current students can find more information on Learn Ultra.