Concepts of Physics

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

Optical activity of sugar solution

Introduction

When a linearly polarized light passes through certain materials, the direction of electric filed is rotated. This phenomena is called optical activity. Among commonly used materials sugar solution shows this phenomena. It can be easily seen with a polarizer sheet.

Apparatus

A laser torch, sugar solution in a plastic box, a polarizer sheet fixed in a stand, a screen

Procedure

  1. Put on the laser torch to get the spot on a white screen. Bring the polarizer sheet in between and rotate it to get the minimum intensity on the screen. Light from ordinary laser torch is linearly polarized to a good extent and hence you can almost stop it by a polarizer.
  2. Without disturbing the laser torch or polarizer, bring the plastic container with sugar solution between them. Use the length of the box. Does the intensity increase?
  3. Rotate the polarizer to get the minimum intensity on the screen in this situation. Estimate the difference between the orientations of the polarizer in the two conditions.
  4. Remove the sugar solution and again set the polarizer to get minimum intensity. Now put the width of the box in the path of the laser. Again rotate the polarizer to get minimum intensity. Estimate the difference between the orientation of the polarizer in the two conditions.

The fact that polarizer has to be rotated to get the minimum again, establishes that sugar solution has rotate the direction of electric filed.

Question: Write the length of the sugar solution and corresponding angle of rotation of the E-field (approximately).