What is Spectrometer?

A spectrometer is an optical device used to study spectra from different sources of light. With the help of a spectrometer, the deviation of light by a glass prism and the refractive index of the material of the prism can be measured quite accurately. Using a diffraction grating, the spectrometer can be employed to measure the wave length of the light. The essential components of a spectrometer are shown in below figure.


It consists of a fixed metallic tube with a convex lens at one end and an adjustable slit, that can slide in and out of the tube, at the other end. When the slit is just at the focus of the convex lens, the rays of light coming out of the lens become parallel. For this reason, it is called a collimator.

Turn Table:

A prism or a grating is placed on a turn table which is capable of rotating about a fixed vertical axis. A circular scple, graduated in half degrees, is attached with it.


A telescope is attached with a vernier scale and is rotatable about the same vertical axis as the turn table. Before using a spectrometer, one should be sure that the collimator is so adjusted that parallel rays of light emerge out of its convex lens. The telescope is adjusted in such a way that the rays of light entering it are focussed at the cross wires near the eye-piece. Finally, the refracting edge of the prism must be parallel to the axis of rotation of the telescope so that the turn table is levelled. This can be tone by using the levelling screws.


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