View Full Version : Mistake in optics lecture

2005-Jan-08, 02:07 PM
I was reading through The Feynman lectures on physics and found a slip in the explanation of Fermat's Principle. The perpendicular drawn to calculate the angle of refraction should be perpendicular to CB not XB to get the correlation but then the trigonmetry doesn't work! So I had a look at the whole thing and the truth is you have to take a perpendicular to the centre line between AC and AX and then the same on the other side. The trig is a whole lot messier but at least it works out to be Snell's law. I had a huge headache with this angle before I discovered Fermat. I got quite close to Snell's law on my own but Feynman's "girl in the water" analogy really cleared things up for me! He really has a way of making complicated stuff clear. I f you disregard the fact that he correlates FCX with BCN' then Fermat's principle could not be made simpler, but if you don't, what then???!
Ferg :)