To practice tactics box 18.1 analyzing refraction. if a ray refracts between medium 1 and medium 2, having indices of refraction n1 and n2, the ray angles θ1 and θ2 in the two media are related by snell's law, n1sinθ1=n2sinθ2. this law becomes a central idea in a procedure for analyzing refraction problems, as explained in the following tactics box. draw a ray diagram. represent the light beam with one ray. draw a line normal to the boundary. do this at each point where the ray intersects a boundary. show the ray bending in the correct direction. the angle is larger on the side with the smaller index of refraction. this is the qualitative application of snell’s law. label angles of incidence and refraction. measure all angles from the normal. use snell's law. calculate the unknown angle or unknown index of refraction. follow the steps above to solve the problem: a diamond is underwater; a light ray enters one face of the diamond, then travels at an angle of 30 degrees with respect to the normal. what was the ray's angle of incidence on the diamond? the index of refraction of water is nwater=1.33, and the index of refraction of diamond is ndiamond=2.42.below is a ray diagram showing the refracted ray as it travels across the diamond. the dashed line represents the normal to the surface between the water and the diamond. complete the diagram by adding the incident ray. even though you don't know the exact direction of the incident ray yet, you can estimate it by applying step 3 in the tactics box above. use your estimate to complete the ray diagram. the location and orientation of the vector will be graded. the length of the vector will not be graded.