Thank-you for taking the time to read my problem. I am currently doing work with light and boundaries and have come accross a question that I am having a hard time understanding. I know how to calculate angles when they go through one boundry but I can not figure out how to do it when there is 2 boundaries. Look at the diagram. Calculate the angle of the emerging ray in air. Assume that the first and second boundaries are parallel. Diagram: http://img27.imageshack.us/img27/6221/scan.jpg [Broken] (thanks to http://www.imageshack.us/ for the free image hosting) I understand the question well. The ray is in air, crosses the boundary into the diamond, and then crosses the second boundary back into air where I have to figure out the angle. Where I am stumped is that second boundary. Thank-you for any help you may be able to give me.