The Hindenburg disaster 6 電流、電阻與電路 The Hindenburg disaster

Outline 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 電路

6-1 電流 電荷守恆 克希荷夫電流(節點)定理

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

6-2 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 ammeter shunts the legal standard for the ohm b [磷] doped to 1023 c [鋁] 1023 as an electrical conductor in cryogenic systems

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

6-3 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

6-4 Semiconductors 半導體

Superconductors 超導體 1911

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

Negative Temperature Coefficient of Resistivity http://www.pnas.org/content/104/34/13565/F5.expansion

6-5 電路 6-5.1 直流電路 6-5.2 串聯電阻 6-5.3 並聯電阻 6-5.4 交流電路 6-5.5 虛擬電路實驗

6-5.1直流電路 Direct Current Circuit A bimetallic strip flasher

Ex.8 簡單直流電路內之電位（電壓）升降 克希荷夫 Kirchhoff 迴路定理

Ex.9 The Ammeter and the Voltmeter

Ex.10 RC電路 電阻－電容電路

Ex.10 (cont) Charging a Capacitor

Ex.10 (cont)

Ex.10 (cont)

Ex.10 (cont) 如果 R = 10M C = 1F 經過46s後，e= 0.01，充電達99﹪ 可用作間歇式雨刷等電路控制。

6-5.2 Resistance in series

6-5.3 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.11 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.12 The electric eel Electroplaque 0.15V 0.25Ω電斑

The Equivalent circuit

The current 0.15V 0.25V Rw=800Ω

6-5.4交流電路 Alternating Current Circuit V( t ) = V0Sin2f 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.13 72W 音箱

Ex.14 A practical example Quebec Montreal

6-5.5虛擬電路實驗