Why Can't There Be a Critical Angle When nB/nA Is Greater Than 1?

AI Thread Summary
The discussion centers on the conditions for critical angles in relation to Snell's Law, specifically when the refractive index ratio nB/nA is greater than 1. It is clarified that a critical angle can only exist when light travels from a medium with a higher refractive index to one with a lower index, which is not the case when nB/nA > 1. The confusion arises from the misunderstanding of how to apply Snell's Law correctly in different scenarios, particularly when comparing transitions between multiple media. The participants emphasize that sinA exceeding 1 is not physically possible, reinforcing the impossibility of a critical angle under these conditions. The conversation highlights the importance of correctly interpreting refractive indices in light propagation scenarios.
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Snell's Law of Angles says that : sinA/sinB = nB/nA

but in order to find critical angles B has to be 90° . I understand that in order to have total internal reflection that nB/nA < 1 but why can't there be a CRITICAL angle when nB/nA > 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 = nwater/nair 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
 
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What do you mean by "if i do it in one go"?
 

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