Snell’s law — UPSC Physics Optional CSE 2006 Paper I

Derive Snell's law of refraction from fermat's principle. How is the refractive index related to the velocity of light ? Light of wavelength 600 nanometre (in vacuum) enters a glass slab of refractive index 1.5. What are the values of wavelength, frequency and velocity of light in glass ? [Velocity of light in vacuum = 3 \times 10^8\text{ ms}^{-1}]