Diamond has an index of refraction of 2.419 and air 1.00. What is the critical angle for a diamond to air surface?

1. Light starting inside the diamond gives n1 = 2.419, and the air outside gives n2 = 1.00. 2. The critical angle is theta_c = inverse sine of (n2 divided by n1) = inverse sine of (1.00 divided by 2.419). 3. The bracket is 0.413, so theta_c = inverse sine of 0.413 = 24.4 degrees. 4. That is a very small critical angle, which is why light struggles to escape once it is inside a diamond. 5. The 11.9 degrees option is the refraction angle for a 30.0 degree ray entering diamond, a different quantity altogether. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.4 Total Internal Reflection_