Concepts of Physics

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

Total Internal Reflection in a Glass of Water

Objective

To see total internal reflection.

Introduction

A ray of light bend away from the normal when it travels from the denser medium to the rarer medium. The angle of refraction increases with increase in angle of incidence. When angle of incidence is more than a particular value, called critical angle, the ray of light is reflected back to the denser medium. This phenomenon is called total internal reflection.

Apparatus

Laser torch, glass of water, white sheet of paper

Procedure

  1. Pass the laser light through the glass of water. You will observe that it passes through the glass. A spot of light will be seen on the white screen kept on other side of the glass.
  2. Now, start bending the torch (in which plane?) so that the ray strike the water surface at an angle. As you go on bending, a point will come when the laser light will be internally reflected from the surface and you will observe the spot of light shifting to the bottom.