Procedure : 

1. Place the semi-circular glass disc in such a way that its diameter coincides with interlace line MM and its center coincides with point O’. 

2. Now send light from the curved side of the semicircular glass disc. 

3. The light travels from denser medium to rarer medium.

4. Start with angle of incidence (i), equals to 0° and observe for refracted on other side of the disc. 

5. It does not deviate into its path when entering rarer medium. 

6. Send laser light along angles of incidence 5°, 10°, 15°, etc. and measure the angle of refraction. 

7. And tabulate the results in the given table. 

Observation : 

• Make a table shown below and note the values ‘i’ and ‘r’.

• At particular angle of incidence, the refracted ray does not come out but grazes the interface separating the air and glass. This angle is called critical angle. 
• When the angle of incidence is greater than critical angle, the light ray gets reflected into denser medium at the interface, i.e. light never enters rarer medium. This phenomenon is called total internal reflection.