11 電磁 IV How did the electric guitar revolutionize rock? From acoustic to electric guitars

Sections 電磁感應 物質的磁性 麥斯威爾方程式 電磁波 Lasers and X-rays

11-1.1 Two symmetric Situations current loop + magnetic field → torque torque + magnetic field → current

11-1.2 Two Experiments First Experiment A Magnet is moving with respect to the loop.

Second Experiment The switch S is closed or opend.

11-1.3 Faraday’s Law of Induction An emf is induced when the number of magnetic field lines that pass through the loop is changing. – A Quantitative Treatment – The magnetic flux

Faraday’s law

例1 A solenoid contains a coil i =1.5 A n = 2.2×104 turns / m A = 3.46 ×10-4m2 N = 130 turns 電流在25ms內穩定降至0

計算 i =1.5 A n = 2.2×104 turns / m A = 3.46 ×10-4m2 N = 130 turns 電流在25ms內穩定降至0

11-1.4 Lenz’s Law Opposition to pole Movement 感應電流所生的磁場與感應出該電流的磁場反向 Opposition to pole Movement Opposition to flux change Electric Guitars

例2 B = 4.0 t2 +2.0 t + 3.0 Ebat = 2.0V r = 0.20m

例3 B = 4 t2 x2 W = 3.0m H = 2.0m t = 0.1s

11-1.5 Induction and Energy Transfers The work done by the applied force and the thermal energy produced in the wire.

The Power

Eddy currents – induction stoves and EM braking

Eddy currents – transformers

Eddy currents –EM braking

Eddy currents – metal detectors

The microphone

The tape recorder

Speaker

Voice-coil positioner of a HDD

11-2.1 Magnetism of Matter How can a clay-walled kiln reveal Earth’s magnetic field of the past? 磁鐵礦(0.3μm)和赤鐵礦(1mm)

11-2.2 The Magnetic field of the Earth The earth’s dipole field The mid-atlantic ridge

11-2.3 Magnetic Materials Diamagnetism (逆磁性) Paramagnetism (順磁性) Ferromagnetism (鐵磁性)

11-2.4 Diamagnetism 逆磁性材料產生之磁矩與外磁場逆向，如外磁場非均勻，其將受到由強磁場區到弱磁場區之斥力。

11-2.5 Paramagnetism 順磁性材料產生之磁矩與外磁場順向，如外磁場非均勻，其將受到由弱磁場區到強磁場區之吸力。 液態氧被吸在兩個磁極之間

11-2.6 Ferromagnetism 鎳的磁域(magnetic domain)

Hysteresis (磁滯)

11-3.1 Maxwell’s Equations

11-3.2 線積分與面積分 (安培迴路和高斯面) 磁場環流量 (安培定律) 電場通量 電場環流量 磁場通量 法拉第定律

11-3.3 Magnets and magnetic flux (磁鐵和磁通量) Magnetic dipole: north/south pole

11-3.4 Gauss’ Law for Magnetic Fields The net magnetic flux thru any closed Gaussian surface is zero.

11-3.5 Gauss’ Law for electric Fields Flux  enclosed charge

11-3.6 Induced Magnetic Fields 3 ways to produce a magnetic field: by an electric current, by a magnetic material, and by induction.

11-3.7 Ampere-Maxwell Law

11-3.8 Displacement Current

11-3.9 Maxwell’s Equations

11-4.1 Electromagnetic Waves The oscillating E and B Fields A Most Curious Wave –The ether (以太)

11-4.2 Characteristics Light  Electromagnetic Waves Hertz (赫茲)– Radio Waves The Electromagnetic Spectrum The Relative Sensitivity of Human eyes 430nm – 690nm

11-4.3 Maxwell’s Rainbow

11-4.4 Comets What shapes the curved dust tail of a comet?

光壓

11-4.5 Polarization (偏振) Polarized Light The Plane of Polarization Linear, Circular and Elliptical polarization

偏振片 1932 polaroid Edwin Land

Polarization of Light

偏振與太陽眼鏡

11-4.6 Liquid Crystal - I

Liquid Crystal - II

Liquid Crystal - III

LCD –Liquid Crystal Display

11-4.7 Reflection and Refraction (反射與折射)

折射率

11-4.8 Chromatic Dispersion – prisms and gratings

Rainbows

11-4.9 Diffraction – (繞射)

狹縫繞射

圓孔繞射 Central maximu and 1st minimum

The Fresnel Bright Spot (1819) Newton Poisson Fresnel

雙狹縫干涉之強度

單狹縫繞射之強度

雙狹縫與單狹縫 Double-slit diffraction (with interference) Single-slit diffraction

X-ray Diffraction

Bragg’s Law

11-5.1 Theory of Lasers Metastable states: 10-3 s vs 10-8 s

He-Ne Lasers He: 20.61eV neon:20.66 eV / 18.70 eV 1.96eV →633nm

Applications of Lasers Barcode scanning, CO2 laser welding and retina surgery

Compact Disc 2t is ½ of a wavelength, Grating used in tracking, pit 0.1 μm

11-5.2 Theory of X-ray

X光繞射與電子繞射

Medical X-rays: CAT

2D and 3D X-ray Images

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