One of my problems reads, 1. Determine the maximum angle for which the light rays incident on the end of the pipe in Figure P35.38 are subject to total internal reflection along the walls of the pipe. Assume that the pipe has an index of refraction of 1.40 and the outside medium is air. http://www.webassign.net/pse/p35-38.gif Now i thought using snells law of refraction would give me the answer by, n1sin(theta)= n2sin(90) and solve for the other sin but this isn't correct. I know that the index of refraction of the air is 1. My other problem goes like, An opaque cylindrical tank with an open top has a diameter of 2.80 m and is completely filled with water. When the afternoon Sun reaches an angle of 27.0° above the horizon, sunlight ceases to illuminate any part of the bottom of the tank. How deep is the tank? For this one I have no idea of how to set it up. My book doesn't even have a section that factors in any type of length measurement into this chapter.