Critical Angle

ZxcvbnM2000

Snell's Law of Angles says that : sinA/sinB = n_B/n_A

but in order to find critical angles B has to be 90° . I understand that in order to have total internal reflection that n_B/n_A < 1 but why can't there be a CRITICAL angle when n_B/n_A > 1 ?

sinA would have to be greater than 1 which cannot happen but if i do it separately : glass to air and water to air and say that air-n-water = n_water/n_air it is 1.33/1.5 which is true but if i do it in one go it is 1.5 / 1.33 . I must be doing something wrong , because this seems too easy :S

Drakkith

What do you mean by "if i do it in one go"?