Now ! Turn on the music! Let the charges move !
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Transcript of Now ! Turn on the music! Let the charges move !
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Now ! Turn on the music!Let the charges move !
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Alessandro Giuseppe Antonio Anastasio Volta(1745-1827)
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zinc Zn →Zn2+ + 2e- sulfuric acid 2H+ + 2e- → H2
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tqi
電流為單位時間流過某一截面積 A 的電荷量!
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Aij
電流密度:單位面積的電流,為空間的區域性質。電流與面積成正比。
定電荷流動的方向為電流密度的方向jj
j
Aji
如果討論的平面不是垂直於電荷流向,
電流即是電流密度對該平面的通量!
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電流也可以是連續的,在不同位置電荷流動的方向可以不一樣,
將曲面切成一個一個的無限小平面,
),,( zyxjj
電流密度是位置的函數
在每一小片平面上,電流都是電流密度對該平面的通量!加總後,通過曲面的總電流就是電流密度對該曲面的總通量
Adji
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歐姆定律
Georg Simon Ohm
在導體中電場與電流成正比!
適用於大片導體內的電流流動jE
ρ 是電阻率 Resistivity ,是材料的性質
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JE
AI
LV
RIIALV
均勻導線內的電流流動
V,I 是比較方便的量!RIV
電流由電位差決定,(導線內部)電位差由電流決定
電阻 R 是一元件的性質
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Copper fcc
Silicon and Carbon
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私人的電子變成公共財產!
電子可以遊走於原子之間!
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能階變成了能帶Energy Band
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Energy Band and Gap
最高層的電子位於未填滿的連續能帶感覺就像在空間之中移動的自由態!
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自由電子模型,在固體中電子很像氣體分子!
電場會使自由電子發生一個淨位移!即使沒有電場,電子也是在導體中如氣體分子般混亂地移動!但總位移為零!
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自由電子模型
meE
mFa
meEavd
平均漂移速度 τ 是兩次碰撞間的平均間隔時間
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𝑣 rms 106 m / s
𝑣d 10− 4 m / s
τ 與外加電場無關,可視為一個常數
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tneAvenALq d )(
dnAevt
qi
dnevAij
由漂移速度可以計算電流
電流密度:單位面積的電流,為空間的區域性質。電流與面積成正比。
取 Δt ,在此時間內通過截面 A 的電荷:
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meEavd
dnevAij
Emnej
2
JnemE
2
歐姆定律
Georg Simon Ohm
jE
ρ 是電阻率 Resistivity ,是材料的性質
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