Concepts of Physics

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

Verification of the Snell's Law Using Semi-circular Disc


The Snell's laws of refraction are,

  1. The incident ray, refracted ray, and normal lies in the same plane.
  2. The angle of incidence \((i)\), angle of refraction \((r)\) and the refractive index of the medium (\(\mu\)) are related by \({\sin i}/{\sin r}=\mu\).

We verify the Snell's law in this experiment.


Semi-circular disc, laser light, white paper, protector, pencil, scale.



  1. Place the semi-circular disc on the paper. Draw its boundary. Find centre of the face and draw normal to it.
  2. Draw three lines making an angle of 30 degree, 45 degree, and 60 degree with the normal.
  3. Place the laser such that incident ray is parallel to one of the line and it strike the semi-circular disc at centre of rectangular face. Observe the refracted light. Mark two points on the path of refracted line and join them. Measure angle of incidence, angle of refraction, and calculate \(\mu\) using formula given above.
  4. Repeat above step for other two angles.
  5. Why incident ray should strike at the centre of rectangular face of semi-circular disc?