1. Why does the sun look a little oval when it is at the horizon?
When the sun is near the horizon, the rays from lower edge are refracted more than those from upper edge due to passage through greater thickness of air. Due to different amount of deviation caused by refraction the shape of sun becomes elliptical or oval-shaped.
2. How does the refraction affects the length of the day?
By refraction the sun remains visible even if below the horizon while rising or setting. Thus the refraction increases the length of the day. Calculations show that sun rises 2 minutes earlier and sets two minutes later due to refraction. As a result the day becomes 4 minutes longer due to refraction.
3. If a metal ball coated with soot, is held immersed into a beaker of water, why does the surface appear silvery.
When the ball is coated with soot, a layer of air is enclosed between the metal ball and the soot. when the light passes through water, it gets totally reflected at the film of air and makes the surface of the ball shiny or silvery.