10 電磁 III How is an aurora so thin yet so tall and wide?

Sections  磁場  電流與磁場

10-1 磁場  The electric field and the magnetic field  Electromagnet s and permanent magnets

The definition of B

The tracks in a bubble chamber

The SI unit for B 1 tesla = 1T =1 N/A ‧ m=10 4 gauss

Magnetic Field Lines Magnetic vs. electric dipoles A horseshoe and a C-shaped magnets

例 1 A 5.3 MeV proton

Crossed Fields: Discovery of the Electron A cathode ray tube Thomson’s procedure: 設定 E = 0, B = 0, 並記錄光點位 置 開啟電場 開啟磁場, 並調至與電場相等

Calculation

Crossed Fields: The Hall Effect By the conduction electrons in copper:

例 2 A cube generator

A Circulating Charged Particle

The frequency and angular frequency Helical Paths 頻率與軌跡

極光橢圓圈

例 3 The Mass Spectrometer ( 質譜 儀 )

Isotope Separation Centrifuge and diffusion chamber 質譜儀

The pitch ( 螺距 ) of the helical path

Cyclotrons and Synchrotrons Fermilab: 6.3km ring ( 迴旋加速器與同步加速器 )

The resonance condition: When proton energy > 50Mev: Out of resonance (relativistic effect) A huge magnet (4×10 6 m 2 ) is needed for high energy (500Gev) protons The proton sychrotron at Fermilab can produces 1Tev proton Synchrotrons

Magnetic Force on a Current-Carrying Wire

For a wire segment: Magnetic Force

例 4 A length of wire with a semicircular arc

Calculation

線圈

Torque on A Current Loop F 2 and F 4 cancel F 1 and F 3 form a force couple

例 5 A galvanometer for analog meters

The Magnetic Dipole The magnetic dipole moments The magnetic potential energy

磁能

10-2 Magnetic Fields due to Currents Conventional rocket EM Rail Gun

Calculating the Magnetic Field due to a current The law of Biot and Savart

Magnetic Field Due to a Current in a Long Straight Wire

Integration

Magnetic Field Due to a Current in a Circular Arc of Wire

例 6 What B does the current produce?

Two Parallel Currents

例 7 The Field Between Two wires

Ampere’s Law Comparing Gauss ’ law and Ampere’s law Ampere’s law

The Magnetic Field Outside a Long Straight Wire with Current

The Magnetic Field Inside a Long Straight Wire with Current

例 7 A hollow conducting cylinder

Solenoids and Toroids Magnetic Field of a Solenoid ( 螺線管 ) Magnetic Field of a Toroid ( 螺線環 )

Magnetic Field of a Solenoid

Magnetic Field of a Toroid

磁圍阻核融合反應器 Tokamak Fusion Test Reactor

A Current Carrying Coil and a Magnetic Dipole A current loop and a bar magnet

Magnetic Field of a Coil

敬請期待 電磁 IV