1. The problem statement, all variables and given/known data The refractive index of diamond is 2.42. A ray of light passing from the inside of a diamond into air makes an angle of incidence of 20 degrees. Find the angle of refraction. 2. Relevant equations n = refractive index aNd = 2.42 (my book said the speed of light in a vacuum and in air are close enough to treat them as the same for our purposes) dNa = 1/aNd Sin i / Sin r = dNa i = 20 degrees 3. The attempt at a solution 0.413 = dNa Sin 20 degrees = 0.3420 0.3420 / sin r = 0.413 therefore 0.3420 x 0.413 = sin r sin r = 0.142 arc sin of 0.142 = 8.159 degrees This is wrong, the answer should be 55.9 degrees.. Where did I go wrong? Did I go wrong in my maths or in my use of the formula? If someone could point me in the right direction that would be wonderful.