Lecture 14, Mar 4

Assigned problem set 7, due after spring break (electromagnetic energy; the blue of the sky).

Demos: (1) disassembled tape player-radio: motor, magnetic head, ferrite antenna; (2) moving-coil loudspeaker and moving-magnet earphones; (3).microwave generator, interference of paths, metallic grating as a polarization filter.

Assigned readings: Bloomfield, sections 12.2 to 12.4; Serway, section 24.1 or equivalent (review); Melissinos, section 4.1;

Monochromatic plane wave solutions of Maxwell's equation. Linear, circular, elliptical and random polarization. propagating waves and standing waves. Electromagnetic energy and energy flux in a wave.

Problem session 7

Taken out and reinserted memory chips on computer motherboard; discussed again various components. Shown MOSFET operation with voltmeter and ammeter hooked up, charging and discharging gate with fingers. Briefly reviewed answers for problem set 5. Answered all questions and exercises on magnetism in Bloomfield, page 458.

Lecture 15, Mar 6

Demo: linear, center-fed antenna: intensity and polarization.

Assigned readings: Melissinos, section 4.2; notes handed out (file antenna.tex).

Electric dipole radiation. Equivalence of a quantum transition to a classical oscillating dipole: as the electron goes from the initial state to the final state it creates, effectively, an electric dipole vibrating with angular frequency and the z component of the dipole moment is given by

Dipole scattering: intensity, angular distribution and polarization. Radiation from a half-wave center-fed linear antenna.

References: assigned readings.

Lecture 16, Mar 18

Phased antenna arrays and basic antenna designs. A Yagi antenna has, typically, one active element (connected to the power supply in broadcasting and to the TV set or radio in reception), and several passive elements, including a reflector and one or more directors, suitably spaced.

Fourier decomposition of a general periodic signal, emphasizing complex exponential formalism:

where T is the period and . Example of square wave; behavior of Fourier series at a discontinuity of f(t) (Gibbs phenomenon).

Assigned readings: Melissinos, section 3.1 and 3.2.

Problem session 7

Examples of Fourier series on the computer. Shown and discussed the guided-wave movie waveguid.mov.

Lecture 17, Mar 20

Assigned problem set 8 (circuits, ionosphere).

Assigned readings: Melissinos, section 4.1; Bloomfield, sections 12.2 to 12.4; Serway, section 24.1 or equivalent (review);

General description of linear oscillations. Equivalence of driven, damped mechanical oscillator with an electric circuit. Solution for the oscillator driven at frequency , using the complex exponential formalism.

Phase coherence and incoherence in emission or scattering from an array (of emitters or scatterers). Diffraction. Incoherent scattering from density fluctuations in a medium: the blue of the sky. Coherent scattering in the forward direction leads to formation of the refracted wave, propagating with speed

(Note: this in SI notation, where and . In the Gauss-cgs system there are no and to mess things up and one uses and to denote and : the index of refraction is then and the speed is still it c/n)

Maxwell's equations in material media: a much simpler description of the formation of waves propagating with speed it c/n.

References: assigned readings; Feynman, chapter 23, especially the Table 23-1 on page I-23-6 (handed out). Note however that we use , while Feynman uses

Lecture 18, Mar 25

Relation of the dielectric constant of a material medium to the properties of the constituent atoms (or free electrons and ions). Optical properties of insulators, metals and plasmas. Reflection of radio waves from the ionosphere.

Reflection and transmission at a flat interface. For normal incidence from vacuum, the reflected and transmitted field amplitudes are and , with

where and ( is the ``vacuum impedance'', Ohm). Note that r+t=1. For a non-magnetic medium this reduces to

where is the index of refraction. The incident intensity is the reflected intensity is and can be written as with the transmitted intensity is and can be written as with Note that R+T=1.

Reference: Melissinos, Sections 4.4 and 4.5.

Problem session 8

Reviewed problems from pledged set. Diffraction and waveguide movies: scattdiff.mov and cavityeh.mov.

Lecture 19, Mar 27

Assigned problem set 9 (fluctuations, Nyquist theorem).

Distributed set of Dorsey notes: the next two lectures follow these closely. See these notes for additional readings.

Waveguides, resonant cavities, optical fibers. Qualitative description, referring to the movies waveguid.mov and cavityeh.mov.

Fourier integrals. Fourier transform of a Gaussian and of a Lorentzian. Reciprocal relation between and , connection with Heisenberg's uncertainty principle. Modulation and demodulation of radio and TV signals.