Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Refractive Index of a Liquid using a Hollow Prism


To find the refractive index of water and saturated salt solution.


The hollow prism, a glass tumbler, chalk piece, laser torch, clamp in which laser can be fixed horizontally, measuring steel tape, Salt, spoon and beaker, sine and tan table


Glass tumbler is to be used as a stand for placing the prism and the wall is to be used as the screen. Clamp the laser at an appropriate height so that the beam can go through the prism placed on inverted glass tumbler. Make arrangement so that the laser, without the prism, falls perpendicularly on the wall. Prism may be placed about 1.5 m away from the wall.


With the laser switch pressed, and putting the hollow prism on the tumbler, mark the spot on the wall. Put water in the prism so that the laser beam goes through water. The spot will shift. Rotate the tumbler about its axis to get the position of minimum deviation. Measure different distances and calculate the angle of minimum deviation. From this calculate the refractive index of water.

Make saturated salt solution and find its refractive index.

Write all the approximations that you have made and an estimate of errors that could result from the approximations.