Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: REFRACTION - REFLECTION



Ok, OK, but how do you explain this to a student when SHE asks:

"When a beam of light enters the surface of water at an angle of
25 degrees with the normal why doesn't it continue at the same
angle after it enters the water? Does Fermat's principle
explain why the wavefront must always perpendicular to the direction
of travel?

Fermat's principle doesn't explain anything. It is a valid
model for the propagation of light, that's all. Physics
doesn't explain; it can only describe. It is a good idea to
keep this fact always in the front of your mind. Not doing so
is the cognitive error which makes the religious believe they
have all the answers.

(Where wavefronts have learned that they must ALWAYS be
perpendicular to the direction of wave propagation)

Better slack off on that a bit, Herb. It is only a requirement
for waves with lightspeed group velocities. In birefringent
materials (calcite, for example) the wavefronts need not be
perpendicular to their directions of propagation.

Leigh