The critical angle for a light ray travelling from a ruby into ethyl alcohol is 50.6 degrees celsius. Determine the index of refraction for ethyl alcohol.

In order to answer this question, I realized that I needed to know the index

of refraction for ruby, so I went and looked it up. It's 1.762 to 1.770.

I started trying to remember how to use this number and the critical angle

to find the index of refraction of the other medium. That's when I saw the

absurd unit "degrees celsius" for the critical angle, and I got discouraged.

But I perked up very quickly, when I realized that I'm still on the "index of

refraction" list, and while I'm there, I might as well just go ahead and

look up ethyl alcohol too.

It's 1.36.