6. Evaluate V. (+) Group-C (Long Answer Type Question) Answer any three of the following 7. (a) What are positive and negative crystals? Give examples. What is optic axis of a crystal? (b) How can you distinguish between circularly polarized light and unpolarized light with help of quarter wave plate and Nicol prism. (c) Explain why light wave can be polarized but sound wave cannot be polarized. (d) Find the state of the polarization when x and y components of the electric fields are given by Ex-E sin (wt+kz) and Ey-o cos (wt+kz). (e) A plane polarized light of wavelength 600 nm changes to circularly polarized light on passing through a quartz crystal cut parallel to optic axis. Calculate the minimum thickness to produce such effect. Given (He Ho)=0.005. 8. (a) Define Magnetic susceptibility and permeability. Obtain the relation between them. (b) Write the differences between diamagnetic, paramagnetic and ferromagnetic substances. (c) What is hysteresis? Draw a hysteresis curve for a sample of iron. Explain the curve step by step.