11 電磁 IV How did the electric guitar revolutionize rock?

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1 11 電磁 IV How did the electric guitar revolutionize rock?
From acoustic to electric guitars

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

3 11-1.1 Two symmetric Situations
current loop + magnetic field → torque torque + magnetic field → current

4 Two Experiments First Experiment A Magnet is moving with respect to the loop.

5 Second Experiment The switch S is closed or opend.

6 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

7 Faraday’s law

8 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

9 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

10 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

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

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

13 11-1.5 Induction and Energy Transfers
The work done by the applied force and the thermal energy produced in the wire.

14 The Power

15 Eddy currents – induction stoves and EM braking

16 Eddy currents – transformers

17 Eddy currents –EM braking

18 Eddy currents – metal detectors

19 The microphone

20 The tape recorder

21 Speaker

22 Voice-coil positioner of a HDD

23 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)

24 11-2.2 The Magnetic field of the Earth
The earth’s dipole field The mid-atlantic ridge

25 11-2.3 Magnetic Materials Diamagnetism (逆磁性) Paramagnetism (順磁性)
Ferromagnetism (鐵磁性)

26 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。

27 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

28 Ferromagnetism 鎳的磁域(magnetic domain)

29 Hysteresis (磁滯)

30 Maxwell’s Equations

31 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

32 11-3.3 Magnets and magnetic flux (磁鐵和磁通量)
Magnetic dipole: north/south pole

33 11-3.4 Gauss’ Law for Magnetic Fields
The net magnetic flux thru any closed Gaussian surface is zero.

34 11-3.5 Gauss’ Law for electric Fields
Flux  enclosed charge

35 11-3.6 Induced Magnetic Fields
3 ways to produce a magnetic field: by an electric current, by a magnetic material, and by induction.

36 Ampere-Maxwell Law

37 11-3.8 Displacement Current

38 Maxwell’s Equations

39 11-4.1 Electromagnetic Waves
The oscillating E and B Fields A Most Curious Wave –The ether (以太)

40 11-4.2 Characteristics Light  Electromagnetic Waves
Hertz (赫茲)– Radio Waves The Electromagnetic Spectrum The Relative Sensitivity of Human eyes 430nm – 690nm

41 Maxwell’s Rainbow

42 Comets What shapes the curved dust tail of a comet?

43 光壓

44 11-4.5 Polarization (偏振) Polarized Light The Plane of Polarization
Linear, Circular and Elliptical polarization

45 偏振片 1932 polaroid Edwin Land

46 Polarization of Light

47 偏振與太陽眼鏡

48 Liquid Crystal - I

49 Liquid Crystal - II

50 Liquid Crystal - III

51 LCD –Liquid Crystal Display

52 11-4.7 Reflection and Refraction (反射與折射)

53 折射率

54 11-4.8 Chromatic Dispersion – prisms and gratings

55 Rainbows

56 Diffraction – (繞射)

57 狹縫繞射

58 圓孔繞射 Central maximu and 1st minimum

59 The Fresnel Bright Spot (1819)
Newton Poisson Fresnel

60 雙狹縫干涉之強度

61 單狹縫繞射之強度

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

63 X-ray Diffraction

64 Bragg’s Law

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

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

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

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

69 Theory of X-ray

70 X光繞射與電子繞射

71 Medical X-rays: CAT

72 2D and 3D X-ray Images

73 再見!