another question to do with snells law, argh

[benhorris]

A student decides to use the tank and water to make a side-show game to raise money at a fete. She places a coin on the bottom of the tank and invites people to drop more coins in to cover it – apparently easy to do until you try it. The water is 0.5 m deep. When someone looks vertically into the tank, how far below the surface does the coin appear to be?

Please help, i have no idea how to do this...

thank you... :-)

[Doc Al]

Consider the coin as a source of light. Follow a ray of light (at some angle \theta to the normal) from the coin through the water and into the air. Which way does it bend when it hits the air? By what angle? So, considering the light from the coin after it gets bent at the surface and hits your eye, where does the coin appear to be? (Extend the ray of light that hits your eye straight back to find the apparent position of the source.)