《直流电路》

1、直流電路 w Direct Current Circuit w A bimetallic strip flasher w 以電阻電熱絲加熱bimetallic strip，約一 秒啟閉一次，可用作警示裝置。 Ex.3-1 Bimetallic Strip Flasher Ex. 3-2 簡單直流電路內之電 位（電壓）升降 iR ViRV aa E E 克希荷夫 Kirchhoff 迴路定理 Ex.3-3 The Ammeter and the Voltmeter Ex. 3-4 RC電路 w 電阻電容電路 Ex. 3-4 (cont) w 如果 R = 10M C = 1F w 經過46s後，

2、e= 0.01，充電達99 w 可用作間歇式雨刷等電路控制。 EECeCtq RC 63. 0)1 ()( /1 s10101010 66 FRC 交流電路 w Alternating Current Circuit w V( t ) = V0Sin2f t w f 頻率 = 60H（赫） w V0 尖峰值， 一般家庭約170V 功率 w P（t）= I0V0Sin2 2 f t，取時間平均值 w 對交流電而言，歐姆定律變成 rmsrmsV I VI VIP 22 2 1 00 00 RIV rmsrms R V RIVIP rms rmsrmsrms 2 2 Ex.3-5 A practic

3、al example Quebec Montreal MW220)1000/22. 0( )A1000( MW0 .55)1000/22. 0( )A500( 368MWV)(500A)1035. 7( 22 2, 22 1 , 5 kmm RIP kmm RIP IP av av av E Ex. 3-5 72W 音箱 V VV Vrms24 2 34 2 0 0 . 3 0 . 8 24V R V I rms rms WVIP rmsrms 72 Automatic Coffee Maker 3-way Light Bulb Electrical Grounding III.2 磁學(Ma

4、gnetism) w 磁場與磁力線 磁性 地磁 w 磁力 磁力與電荷的運動 載流導線 電流所產生之磁場 物質之磁性 磁性 w 同極相斥，異極相吸 指南針順磁場排列 or 鐵砂順磁場排列 磁力線 w 磁單極 地磁 The earths dipole field The mid-atlantic ridge 太陽風與地磁 w 地磁如同來自一磁棒，其軸與地球自轉 軸之夾角目前為11.5 w 地球在太陽風中以超音速（0.01of C ） 前進，產生弓形震波（bow shock） 在太陽風吹襲下的地磁 磁層 古代的磁場 wHow can a clay-walled kiln reveal Earths

5、magnetic field of the past? 磁力與磁場 BvqF B The SI unit for B 1 tesla = 1T =1 N/A m=104 gauss 電子槍 電子質荷比 yE LB q m BEv qvBqE mv qEL y 2 , / , 2 22 2 2 磁力與電荷的運動 qBm vrT qBmvr rmvqvB rmvmaF /2 /2 / / / 2 2 迴旋頻率 w The frequency and angular frequency uHelical Paths 2 2 1 m qB f m qB T f sin cos 11 vvvv 螺線運動

6、與磁瓶 qB m vTvp 2 cos 11 螺距 wThe pitch (螺距) of the helical path 極光橢圓帶 Earth as a dipole field Van Allen Belt Magnetic Mirror Charged Particles from the Sun Auroras: the Northern and Southern Lights UV and X-ray emissions from Aurora UV emission from northern aurora observed by the Polar satellite X-ra

7、y emission from northern aurora observed by the Polar Satellite The Mass Spectrometer 2 21 /2 2 1 2 rx q mV BqB mv r mqVv qVmv u93.203 8 22 2 22 V qxB m q mV B rx Isotope Separation Centrifuge and diffusion chamber 質譜儀 同位素分離 迴旋加速器 (cyclotrons) w 迴旋頻率不因 速率增加而改 變，因此可用 定頻交流電持 續加速） wThe resonance condit

8、ion: wWhen proton energy 50Mev: Out of resonance (relativistic effect) A huge magnet (4106 m2) is needed for high energy (500Gev) protons wThe proton sychrotron at Fermilab can produces 1Tev proton osc ff 同步加速器 (synchrotrons) Fermilab 6.3km Tevatron 載流導線 載流導線所受的磁力 BLiF iLBBqvF viLitq B dB d sin / 載流

9、線圈 Speaker Voice-coil positioner of a HDD MHD Propulsion Maglev Trains EM Rail Gun Magnetic Resonance Imaging III.3 電磁感應 wTwo symmetric Situations current loop + magnetic field torque torque + magnetic field current wTwo Experiments wApplications First Experiment wA Magnet is moving with respect to

10、the loop Second Experiment The switch S is closed or opened Faradays law w An emf is induced when the number of magnetic field lines that pass through the loop is changing 2 m1T=1Wb =1Weber A dB B turns)(N dt d N dt d B B E E A Simple Example RBlvi BlvdtBldx dtBlxddtd BlxBAFvP / / / )(/ , RvLBRRBLvRiP RvLBFvP RvLBiLBF /)/( / / 22222 222 22 Magnetic Tape Recording Electric Guitar The Playback Head The moving-coil microphone Tr