Introduction to Modern physics Dr. E.J. Zita, The Evergreen State College, 9.Jan.03 Lab II Rm 2272, Overview Ch.1: Particles and Waves ML1: Cyclotron motion ML 2: Bainbridge Mass Spec Ch.2: Special Relativity ML 3: Relativistic momentum

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)

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

1.1 Classical Particles Classical mechanics: Force completely describes a system: Use F=ma = 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

ML1: Cyclotron motion

1.2 Discovery of the Electron Thomson measured charge/mass ratio (1897) with E and B fields Electron beam deflected by  :

Millikan oil drop experiment determined m and e (1909) Ex. 12: Find v 1 =x 1 /t 1 =________, E=  V/  x Solve for m: For each data point, find v 2 =x 2 /t 2 and q.

ML 2: Bainbridge Mass Spectrometer Crossed E and B fields select velocity: Trajectory curves with r cyclotron in B’ field where E=0

1.4 Classical Waves Transverse wave moving to the right with amplitude A: where wavenumber k=2  frequency w=2  /T, phase =  Information travels with group velocity: Ex: Ch.1 #30

Waves: Interference and Diffraction Interference maxima where d sin  = n (d = slit separation, n=integer) Diffraction minima where a sin  = m   a = slit width, m=odd) X-rays: Bragg scattering maxima where 2d sin  = n

Electromagnetic waves travel at the speed of light c (Maxwell 1873)

Ch.2: Special Relativity To an observer at rest, an object moving at v close to c has its * length L contracted to L/  * time dilated (stretched) to  T * momentum and energy also increase by factor  Ex: Muons moving with v=0.9994c have  At rest in the lab frame, muon lifetime T=2 x s. Fast muons created in the upper atmosphere would not live long enough to be detected on Earth’s surface, classically. But time dilation lets them live 23 times longer (from our perspective), so they are indeed detected on the ground.