To get total internal reflection at the interface of water (refractive index 1.33) and a plastic whose refractive index is 1.46: (a) Which material must the light start in? (1) It doesn't matter...

To get total internal reflection at the interface of water (refractive index 1.33) and a plastic whose refractive index is 1.46:

(a) Which material must the light start in?

(1) It doesn't matter