What is the danger if your hair suddenly stands up? 9 電磁 II Sequoia 紅杉 What is the danger if your hair suddenly stands up?
本單元內容 9-1電位與電容器 9-2電流與電阻 9-3電路
9-1.1 電位能 Fe and Fg are mathematically identical Fe is a conservative force
9-1.2 電位 Ue depends on q, but Ve does not
9-1.2 等位面 Four Equipotential Surfaces
9-1.3 等位面3例 E.S. for a uniform field, a point charge, and an electric dipole
9-1.4 由電場算電位 The differential work done by F
Ex. 1 均勻電場 (a) Along path (a)
Ex. 1 均勻電場︰路徑(a)
Ex. 1 均勻電場︰路徑(b)
9-1.5 點電荷的電位
點電荷的電位
點電荷的電位圖
9-1.6 一組點電荷的電位 The principle of superposition
Ex.2 12 electrons on a circle on an arc
9-1.7 電雙極的電位
雙極矩 p = qd p 由負電荷指向正電荷
Induced Dipole Moment 感應雙極矩 極化 (polarization)
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
水分子與微波爐
9-1.8 連續電荷分佈的電位
Line of Charge
計算
Charged Disk
計算
9-1.9 由電位算電場 The work done by the electric field
Ex.3 The charged disk
9-1.10一組點電荷的電位能 For charges q1 and q2 Ex.4 Three charges
Ex.5 An alpha particle and a gold nucleus Femto 10-15
9-1.11 Potential of a charged isolated conductor 導體內部及表面為一等位面(equipotentail surface)
Discharge
Plots of E (r) and V(r)
9-1.11 電容器 電容（Capacitance） 平行板電容器 C = ( F 法拉 ) K: 介電常數，真空 = 1 0: 真空電容率 A: 板面積 d : 兩板距離
Ex.4 1.0 F 電容器 d = 1.0mm
9-1.12 Capacitors in parallel
等效電容
9-1.13 Capacitors in series
等效電容
Ex.5 A RAM Chip C = 55fF（10-15） V = 5.3 volt A charged capacitor means that a “one” has been stored. http://computer.howstuffworks.com/question452.htm
Ex.6 電容式鍵盤
Ex.6 (cont) A = 9.50 10-5m2 ; k = 3.50 按鍵後d由5.00mm減為0.150mm 按鍵前 C = 0.589PF
電容式麥克風
Ex.7 defibrillator (除纖顫機)
心跳停止病人之急救 盡快求助 盡快給予先進的救命治療 盡快實行心肺復甦術(CPR) 盡快除纖顫
人體各部位的電位差 人體的肌肉及神經細胞利用鈉、鉀等正離子及氯負離子執行生化機能；因此造成之電場延伸至人體表面，形成小量之電位差。 心電圖 -電極置於不同位置（A-B，B-C等）即決定不同形狀的心電圖。 腦波圖 -電極置於頭部特定部位，紀錄電位差隨時間之變化。
心電圖和腦波圖 EKG EEG
視網膜電圖 ERG
9-2 電流與電阻 電流、電流密度與漂移速度 電阻與電阻率 歐姆定律 半導體與超導體
9-2.1 電流 電荷守恆 克希荷夫電流(節點)定理
9-2.2電流密度 J: A/m2
電流密度與漂移速度
銅的漂移速度 dAl=2.5mm, dcu=1.8mm i=17mA, ρ=9×103kg/m3,M=64×10-3kg/m3
9-2.3 電阻與電阻率 Resistance Resistivity Conductivity
電阻率 a 銅為主的合金,包含了12%的錳和4%的鎳 b [磷] doped to 1023 c [鋁] 1023
電阻的計算 Bad Boys Ravish Only Young Girls But Violet Gives Willingly
溫度效應 293K-1.69x10-8
The effect of temperature
電阻的微觀意義
9-2.4 Ohm’s Law 流過一電路元件之電流與該元件之電位差成正比 電阻率與電場的大小及方向無關
I-V curves conductor pn junction diode
Semiconductors 半導體
Superconductors 超導體
More Maglev - magnetic levitation http://web.mit.edu/physics/hudson/ResearchBackground.htm
Maglev、MRI and Tevatron 1. The new test line called the Yamanashi Maglev Test Line opened on April 3, 1997 On April 14, 1999, this five-car train set surpassed the speed record of the three-car train set, attaining a maximum speed of 552 km/h in a manned vehicle run. On December 2, 2003, a three-car train set (JR-Maglev MLX01) attained a maximum speed of 581 km/h (361 mph) in a manned vehicle run. 2. Fermilab: 6.5 kM 1 TeV
Power line and motor 1. In May of 2001 some 150,000 residents of Copenhagen, Denmark, began receiving their electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes. In the summer of 2001 Pirelli completed installation of three 400-foot HTS cables for Detroit Edison at the Frisbie Substation capable of delivering 100 million watts of power. 2. 5000 horse-power motor
BCS Theory - The Cooper pairs the Nobel Prize in 1972 BCS theory predicted a theoretical maximum to Tc of around 30-40K
9-3 電路 直流電路 串聯電阻 並聯電阻 交流電路 虛擬電路實驗
9-3.1直流電路 Direct Current Circuit A bimetallic strip flasher
Ex.8 Bimetallic Strip Flasher
Automatic Coffee Maker
Ex.9 簡單直流電路內之電位（電壓）升降 克希荷夫 Kirchhoff 迴路定理
Ex.10 The Ammeter and the Voltmeter
Ex.11 RC電路 電阻－電容電路
Ex.11 (cont) Charging a Capacitor
Ex.11 (cont)
Ex.11 (cont)
Ex.11 (cont) 如果 R = 10M C = 1F 經過46s後，e= 0.01，充電達99﹪ 可用作間歇式雨刷等電路控制。
9-3.2 Resistance in series
9-3.3 Resistors in parallel
Multiloop Circuits The Junction rule: 流入接點之電流必等於流出者 (Kirchhoff’s junction/current rule)
解System of equations (聯立方程組)
Ex.12 What are the currents?
解聯立方程組 pivot equation
高斯消去法 Forward Elimination and Back substitution pivot equation upper triangle Forward Elimination and Back substitution
Ex.13 The electric eel Electroplaque 0.15V 0.25Ω電斑
The Equivalent circuit
The current Rw=800Ω
9-3.4交流電路 Alternating Current Circuit V( t ) = V0Sin2f t f 頻率 = 60H（赫） V0 尖峰值， 一般家庭約170V
功率 P（t）= I0V0Sin2 2 f t，取時間平均值 對交流電而言，歐姆定律變成
Ex.14 72W 音箱
Ex.15 A practical example Quebec Montreal
3-way Light Bulb
Electrical Grounding 0.001A : Mild tangling sensation 0.01-0.02A: Muscle spasms 0.2A: fatal (fibrillation) The skin resistance may vary from 1000 ohms for wet skin to over 500000 ohms for dry skin
9-3.5虛擬電路實驗
敬請期待 磁學(Magnetism)
架設
毛髮直豎
內部構造
Negative Temperature Coefficient of Resistivity http://www.pnas.org/content/104/34/13565/F5.expansion