(a) (i) A plane light wave propagating from a rarer into a denser medium, is incident at an angle $i$ on the surface separating two media. Using Huygen's principle, draw the refracted wave and hence verify Snell's law of refraction. (ii) In a Young's double slit experiment, the slits are separated by $0.30\text{ mm}$ and the screen is kept $1.5\text{ m}$ away. The wavelength of light used is $600\text{ nm}$. Calculate the distance between the central bright fringe and the $4^{\text{th}}$ dark fringe.