Christopher Crawford 2015-01-14 PHY 417G: Introduction Christopher Crawford 2015-01-14.

PHY 417G: Introduction

Christopher Crawford2015-01-14

Outline• Announcements

Syllabus; schedule: HW due, recitationsGrades – distribution, Feedback – discussionREU opportunities – ex: accelerator physics

• IntroductionRidiculously brief history of E&MMath review: linear + differential spaces, fund. theoremsE&M review/overview: mathematical structure

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Announcements

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• Syllabus: pa.uky.edu about courses 417– HW schedule: recitations?, due day? Office hours? Exams?

• Grades: Final Grade Final Exam

• Feedback– Your participation in class changes everything!

• REU positions– http://www.anl.gov/education/undergraduates/internship-opportunities/l

ee-teng-undergraduate-fellowship-accelerator

History of magnetism• The magnetic force was known in antiquity

– Magnetism more predominant in nature but more difficult to quantify:1. Permanent magnets (magnetization), not electric currents2. No magnetic (point) charge (monopole) –> dipole effect (N,S poles)3. 1-d currents instead of 0-d charges –> can’t split a wire!4. Static electricity produced in the lab long before steady currents

• Timeline (from “A Ridiculous Brief History of Electricity and Magnetism”) – 600 BC Thales of Miletus discovers lodestone’s attraction to iron– 1200 AD Chinese use lodestone compass for navigation– 1259 AD Petrus Peregrinus (Italy) discovers the same thing– 1600 AD William Gilbert discovers that the Earth is a giant magnet– 1742 AD Thomas LeSeur shows inverse cube law for magnets– 1820 AD Hans Christian Ørsted discovers that current twists magnets

Andre Marie Ampere shows that parallel currents attract/repel Jean-Baptiste Biot & Felix Savart show inverse square law

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Unification of 4 Fundamental Forces

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Classical Fields

• action at a distance vs. locality• field ”mediates “carries force• extends to quantum field

theories• field is everywhere always E (x, t)• differentiable, integrable • field lines, equipotentials

• powerful techniques for solving complex problems

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Magnetic fields• In magnetism it is more natural to start with the concept of

“Magnetic field” than the actual force law! (dipole)

• Compass alignswith B-field

• Iron filings lineup along magneticfield lines

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• Magnetic field lines look like an electric dipole (in fact the magnetic dipole was discovered first!)

Difference between E, B dipoles• Same as the differences between Flux and Flow!

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• Charge = sources of flux• Conservative flow [potential]• Example: Amber (electric)

– Rub to charge– 2 charges (+/–) “monopole fluids”– Exerts force on charges

• Continuous field lines [flux]• Rotational (source of flow?)• Example: Lodestone (magnet)

– Always charged– 2 poles (N/S) “inseparable dipole”– Exerts torque on other magnets

Formulations of E & M• Electricity Magnetism

• Note the interchange of flux and flow: twisted symmetry!

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Magnetic scalar potentialElectrostatics – Coulomb’s law Magnetostatics – Biot-Savart law

B.C.’s: Flux lines bounded by charge Flux lines continuous Flow sheets continuous (equipotentials) Flow sheets bounded by current

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L/T separation of E&M fields

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Equations of Electrodynamics

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Polarization & Magnetization• Chapter 4: electric materials –> Chapter 6: magnetic materials

• Polarization chain –> Magnetization mesh

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3 Materials –> 3 Components• Materials constants: permittivity, resistivity, permeability• Electrical components: capacitor, resistor, inductor• Each is a ratio of Flux / Flow !

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