The book I'm currently reading describes an interesting experiment with polarized light. I'd like to try it but it requires three polarizers and I don't have that many.
It goes like this:
Photons are polarized; either vertical, horizontal, or something in between (actually, according to quantum theory they are not polarized until you measure them). However, if you pass light through a verticaly polarized filter, you will see light coming through that is only vertically polarized. All photons with different polarizations will be blocked (well, almost all). If you then place a horizontally polarized filter after the vertical one, virtually all of the light will be blocked. Makes perfect sense.
However..... if you then place a filter polarized at 45 degrees between the other two, light will come through all three filters. The book I'm reading says that all of the light will come through but that is not quite right, it is actually only 1/2 ,(i.e cos 45 squared). But light does come through. Remove the center filter and the light stops. If you want an interesting discussion of (not an explanation of) this phenomenon, there is a reasonable one at: http://www.mtnmath.com/whatrh/node78.html
Another interesting experiment involving polarized light is to send photons polarized at +45 degrees through a calcite crystal. The crystal will split into the light into two streams, one horizontally polarized, the other vertically polarized. If you then intercept these two streams of light with a second calcite crystal, they will be combined to produce a single light stream again polarized at +45 degrees. All good so far.
If, however, you send the photons through the two crystals only one at a time, you will still get a +45 degree photon out of the second crystal.
There is an interesting discussion of this one at:
http://quantumweird.wordpress.com/quantum-weirdness-a-matter-of-relativity-part-3/
No comments:
Post a Comment