Measurement of refractive index of a glass or perspex block
AIM:
The aim of this experiment is to measure the refractive index of glass (or Perspex).
20
10
0
10
20
30
30
40
40
50
50
60
60
i
70
70
80
80
A
90
90
80
80
70
70
r
60
60
50
50
40
40
30
30
20
10
0
10
20
i
sin i r sin r
(n)
20o
30o
40o
50o
60o
70o
B
Take a rectangular block and draw round it on the paper marked with a protractor.
Shine a ray of light onto the centre of one long face at an angle of incidence (i) of 40o.
Record carefully how it travels through the block and measure the angle at which it leaves the other
side of the block.
Repeat this procedure for a series of angle of incidence (i) from 20o to 70o.
Calculate the values of sin i and sin r for each pair of angles and then work out the mean value for the
refractive index (n) of the acrylic block.
Refractive index = sin i/sin r.
If the protractor sheet is not available make the normal line to the block at A and Mark the point of
emergence of the light (B). After removing the block join points A and B and then measure the angle
of refraction (r).