Physics 3220 - Notes, lecture 1 (Mon, Aug 26, 1996)

Introduction, discussion of syllabus

What is quantum mechanics (vs. what is classical mechanics?)

Breakdown of classical physics, Blackbody radiation.

Next lecture: Planck's resolution of blackbody radiation, more breakdowns of classical physics: Photoelectric, Compton scattering...

SPECIAL NOTE ON UNITS

When possible, we will use cgs units (cm, grams, seconds are the basic units) but sometimes other units like angstroms and eV's.

Here's a summary of the most important units and constants we'll use:

1 eV = 1 electron volt = K.E. acquired by electron accelerated through a potential of 1 Volt:

1 ev = 1.602 * 10^-12 erg (unit of energy)

1 A = 1 Angstrom = 10^-8 cm (unit of length)

1 F = 1 Fermi = 1 femtometer = 10^-13 cm (unit of length)

1 amu = 1 atomic mass unit = 931.5 MeV = 1.49 * 10^-3 erg

m_e = electron mass = 0.511 MeV = 8.19*10^-7 erg

(Note: the last two are energies on the rhs, but the lhs is a mass!! We are sneakily assuming the formula E=mc^2, so I multiplied t he electron mass by c^2 to get the right side) Of course,

c = speed of light = 3*10^10 cm/s

More on units:

= "h-bar" = Planck's constant/(2 Pi) = h /(2 Pi)

= 6.626*10^-27 erg sec/(2 Pi) = 1.054*10^-27 erg sec

c (= hbar c) has units of [erg cm] = [energy length],

c = hbar c = 200 MeV fm = 2000 ev Angstroms. (Handy to remember!)

Charge of an electron, e = 4.803 *10^-10 esu (cgs)

I'll try to stick to cgs units when dealing with E+M, so there are no 's, and for example

(units on that last equation are

[dynes] = [esu * statvolts/cm] + [esu * (cm/sec) * gauss / (cm/sec)]

Note that e^2/r is an energy (potential energy of two electrons, r apart!)

so [e^2] = [energy * length] = [ c] * (some number)

In cgs units, e^2/( c) = 1/137 = , the fine structure constant

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