Presentation on theme: "NASSP Self-study Review 0f Electrodynamics"— Presentation transcript:
1NASSP Self-study Review 0f Electrodynamics Created by Dr G B Tupper
2The following is intended to provide a review of classical electrodynamics at the 2nd and 3rd year physics level, i.e. up to chapter 9 of Griffiths book, preparatory to Honours.You will notice break points with questions. Try your best to answer them before proceeding on – it is an important part of the process!
19QuestionsA monochromatic plane-polarized wave propagating in the z-direction has Cartesian components in phase:.In contrast, a circularly-polarized wave propagating in the z-direction has Cartesian componentsout of phase:Describe in words what such a circularly-polarized wave looks like. One of the two casess “left-handed”, and the other is “right handed” – which is which?iDetermine the corresponding magnetic field.Determine the instantaneous energy-density and Poynting vector.
20Electrostatics in matter Electric field polarizes matterPotential in dipole approximationBound charge densityPolarization: dipole momentper unit volume
21Electrostatics in matter Rewrite Gauss’ lawDisplacement fieldFor linear isotropic mediaFree charge density
40QuestionsWhat one calls a “good conductor” or “good insulator” is actually frequency dependant; i.e. isor ?Find the value of for pure water and for copper metal. Where does it lie in the electromagnetic spectrum in each case?For each determine the high-frequency skin depth.For each determine the skin depth of infrared radiation ( ).In the case of copper, what is the phase velocity of infrared radiation?In the case of copper, what is the ratio for infrared radiation?
41Frequency dependence Electric field polarizes matter …dynamically Model…dynamicallyDamping (radiation)“Restoring force”Driving force
42Frequency dependence Electromagnetic wave Rewrite in complex form Steady state solutionNatural frequency
43Frequency dependence Substitution of steady state solution Dipole moment
44Frequency dependence Polarization Complex permittivity Number of atoms/molecules per unit volume
45Frequency dependence Even for a “good insulator” Low density (gases) Absorption coefficientIgnore paramagnetism/diamagnetism
49Electromagnetic waves in Plasma Electrons free to move; inertia keeps positive ions almost stationaryModelSolutionElectron massNo restoring force!
50Electromagnetic waves in Plasma Current densityConductivityElectron number densityDrude model
51Electromagnetic waves in Plasma Electron collisions rare, so dissipation smallRecall for conductorPurely imaginary!!
52Electromagnetic waves in Plasma Above the plasma frequency: waves propagate with negligible lossBelow the plasma frequency: no propagation, only exponential dampingDispersion relationPlasma frequencyF&F 2013 L46