Optical activity — UPSC CSE 2006 Physics PYQ

What is optical activity ? Give reasons for the conclusion that optical rotation in liquids has a molecular origin. What do you mean by ordinary and extraordinary rays ? What are positive and negative crystals ? Give an example of each. Compute the minimum thickness of a quarter-wave plate made from quartz for incident wavelength of 589.3 nanometer. Given \mu_o = 1.544 and \mu_E = 1.553.