Question

How will you determine refractive index of material of prism using a spectrometer.

Answer 1

You can use the minimum deviation formula to calculate refractive index of the material of prism.

The relationship between minimum deviation and refractive index is given by
$\mu =\frac{\sin \left({\displaystyle \frac{A+{\delta }_m}{2}}\right)}{\sin \left({\displaystyle \frac{A}{2}}\right)}$

First switch on the source of the spectrometer. Then measure the angle of the rotating table directly keeping eyepiece in front of the collimator. This will give you the direct angle. Now place the prism on the rotating table. Make sure that centre of prism is directly above the rotational axis of the rotating table. Now rotate the table to get the minimum deviation. If you rotate the table, in one direction the deviation will decrease. If you keep rotating table in the same direction after a particular point the deviation will start increasing again. This particular point is the minimum deviation. Note down the angle. The difference in the angle give you the minimum deviation say ${\delta }_m$. Knowing angle of the prism A, (may be supplied by the company or you can measure simply drawing the prism on a paper and measure using a protector) you can now easily calculate the refractive index.