Question

How do you find experimentally the refractive index of material of a prism?

Answer 1

Hint For this experiment, take a triangular prism of specified length and normal or colored pins. Place it on a wooden table and note the deflected image carefully. Place pins on the deflected point and draw the line. Use a refractive index formula to get the exact value.

Complete step by step answer
Take a triangular based glass prism and place it on the white paper on a wooden stool or table in such a way that the triangular base of the prism is placed on the chart. Using a pencil draw a line around the prism. Assign name to its vertices A, B and C.
 Now using a protractor,find the angle between AB and BC. This is said to be the angle of the prism. Mark a point L on the side of triangle AB and draw a perpendicular line to the AB touching point L. Now, keep protractor center at point L and along the normal line mark an angle of \[{30^ \circ }\] and connect the line to point L.
 The angle made by the line joining L and the side of the prism is the angle of incidence. After this, place the triangular base prism on its outline. On the side of incident line, fix two pins erect on the line at point P and point Q. Look at the other vertex of the prism for the images of pins and fix another two pins at two points R and S such that all the four pins placed appear collinear and in straight line.
 Take the prism and remove the pins. Connect points R and S, such that it meets vertex AC at a point. The angle formed between the normal of the prism and the line joining P and S is called the angle of emergence.
 Join point L and normal N. Now the pathway of light ray is provided by the points P,Q,L,N, R and D. Extend both incident ray and the emergent rays till they intersect at a point J. The angle between the incident and the emergent ray is called angle of deviation.
Repeat the experiment for various incident ray angles and use the formula,

\[\mu = \dfrac{{\sin [\dfrac{{(O + J)}}{2}]}}{{\sin \dfrac{O}{2}}}\], where O is angle of prism and J is angle of deviation

Note Refractive index of a material is a dimensionless quantity which defines the speed of light that can travel through from one medium to another. It also measures the bending of light rays, as it progresses from one medium to another.