Class Notes, Spring 2002

 Week of Jan 14 Feb 4 Mar 4 Apr 1 Phy 360 page Jan 21 Feb 11 Mar 18 Apr 15 Jan 28 Feb 18 Mar 25 Apr 22 Feb 25

Phy 360, Week 6

20 Feb Louis deBroglie had the idea that if light (a wave) has particle properties then could it be that electrons (particles) have wave properties? I tried to show how you could plausibly conjecture this and then plausibly conjecture the equations to describe it.

p = h / l         E = h f         E = p2 / 2 m

For the sort of energy that an electron in a TV set has, compute the wavelength. It comes out at a small fraction (.01 or so) of an atomic diameter. To raise the wavelength to the size of an atom, you have to decrease the energy by a factor of 10000.

Davisson and Germer found confirming evidence of deBroglie's hypothesis, thought they weren't looking for it. Since then it has been verified at every level.

How can a particle "be" a wave? How can a wave "be" a particle? The resolution of those questions require understanding the concept of probability and then of probability density. We spent some time pinning these down.

22 Feb Wave interference. Demonstrate the phenomenon with light through a diffraction grating and then through a double slit. Set up the equations to describe the wave passing through a double slit. (HW: finish using the trig identity and interpret the results.)

Next: How can you understand this phenomenon in terms of particles? I described what happens if you do the double slit experiment at very low intensity. The particles come through one at a time, but after an accumulation of many particles the overall picture looks like the one predicted by the wave theory. I can describe this phenomenon in terms of a probability density. There is an underlying wave theory that predicts this probability density in terms of the (absolute) square of a wave.

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