Introduction to Modern physics Dr. E.J. Zita, The Evergreen State College, 9.Jan.03 Lab II Rm 2272, [e-mail], 360-867-6853

1
Introduction to Modern physicsDr. E.J. Zita,
The Evergreen State College, 9.Jan.03Lab II Rm
2272, zita_at_evergreen.edu, 360-867-6853
Overview Ch.1 Particles and Waves ML1
Cyclotron motion ML 2 Bainbridge Mass
Spec Ch.2 Special Relativity ML 3
Relativistic momentum
2
Overview of Modern Physics

• 1. Particles and Waves in classical physics
• 2. Special Relativity
• 3. Quanta of Energy
• 4. Atomic structure and spectral lines (QM.4)
• 5. Wave mechanics 1 free particles (QM.1-3)
• 6. Wave mechanics 2 particles in potentials
  (QM.2-4)
• 7. Spin and the Pauli exclusion principle
  (QM.4-6)
• (11. Nuclear transmutations)
• (12. Elementary particles)

3
Ch.1 Particles and Waves
Light interferes and diffracts - but so can
electrons, in Ni crystal
Electrons can scatter like little billiard balls
- but so can light, in the photoelectric effect
4
1.1 Classical Particles
Classical mechanics Force completely describes
a system Use Fma m dp/dt to find x(t) and
v(t).
For time-dependent forces a(t) F(t)/m
v(t) ? a(t) dt x(t) ? v(t) dt For
space-dependent forces F(x) ma m dv/dt
where dv/dt dv/dx dx/dt v dv/dx ?v dv 1/m
?F dx
5
ML1 Cyclotron motion
6
1.2 Discovery of the Electron
Thomson measured charge/mass ratio (1897) with E
and B fields
Electron beam deflected by q
7
Millikan oil drop experiment determined m and e
(1909)
Ex. 12 Find v1x1/t1________ , EDV/Dx Solve
for m For each data point, find v2x2/t2 and q.
8
ML 2 Bainbridge Mass Spectrometer
Crossed E and B fields select velocity
Trajectory curves with rcyclotron in B field
where E0
9
1.4 Classical Waves
Transverse wave moving to the right with
amplitude A where wavenumber k2 p/l frequency
w2 p/T, phase d Information travels with
group velocity Ex Ch.1 30
10
Waves Interference and Diffraction
Interference maxima where d sinq n l (d
slit separation, ninteger) Diffraction
minima where a sinq m l (a slit
width, modd)
X-rays Bragg scattering maxima where 2d sinq n
l
11
Electromagnetic waves travel at the speed of
light c (Maxwell 1873)
12
Ch.2 Special Relativity
To an observer at rest, an object moving at v
close to c has its length L contracted to L/g
time dilated (stretched) to g T momentum
and energy also increase by factor g Ex Muons
moving with v0.9994c have g29. At rest in the
lab frame, muon lifetime T2 x 10-6 s. Fast
muons created in the upper atmosphere would not
live long enough to be detected on Earths
surface, classically. But time dilation lets
them live 23 times longer (from our perspective),
so they are indeed detected on the ground.