1. The problem statement, all variables and given/known data A pair of students measure the refraction of light in passing from acetone into air for several angles. When the angle of incidence is 30, the angle of refraction is 42. b) What is the angle of incidence (in degrees) when the refracted angle is the critical angle? 2. Relevant equations Snells law: Ni*sin(i)=Nr*sin(r) 3. The attempt at a solution I found the index of refraction for air to be 1 and for acetone to be 1.36. By snell's law setting r=90: sin(i crit) = nr/ni * sin(90) = nr/ni = 1/1.36 icrit = arcsin(1/1.36) = 55.73 degrees Is my answer correct? I'm a bit confused about the part that says "...when the refracted angle is the critical angle". Isn't the angle of incidence (when it creates a refraction of 90 degrees) the critical angle?