6 電流與電阻

The Hindenburg disaster

6 電流與電阻

6-1 電流、電流密度與漂移速度 6-2 電阻與電阻率

6-3 歐姆定律

6-4 半導體與超導體

Contents

6-1

C/s)

= A amp ere;

(

dt i  dq

2 1

0

i i

i  

•

克希荷夫電流(節點)定理

電流密度

A J i

JA dA

J JdA

i

A d J

i



















 ^{ }

J: A/m²

電流密度與漂移速度

d d

d d

d

v ne ne J

J nAe

v i

v nAev L

nALe t

i q

v t L

e nAL q

 

) (

, / =

=

, ) (













銅的漂移速度

mm/h 88

. 1 m/s

10 9

. 4

m electrons/

10 47

. 8

mass/mol mass/m atoms/mol

atoms/m or

7

3 28

3 3





















ne v J

M n N

M N

n

d

A A





2 3

2 3

2 6

2

/ 10

7 . 6 /

/ 10

5 . 3 /

10 91

. 4 )

2 / (

m A

A i

J

m A

A i

J

m d

A

Cu Cu

Al Al

Al





















d

=2.5mm, d

=1.8mm

kg/mol

6-2

•

•

•

E J

J E









電阻率

Figure 25.4

UnFigure Page 824

Resistivity and temperature

• Resistivity depends on

temperature. See Figure 25.6 at the left.

• Table 25.2 shows some

temperature coefficients of resistivity.

Symbols for circuit diagrams

• Table 25.4 shows the usual symbols used in circuit diagrams.

Resistors are color-coded for easy identification

• This resistor has a resistance of 5.7 kΩ with a tolerance of ±10%.

電阻的計算

A R L

L R A A

i

L V

J E

A i

J L

V E



     





/ /

/ ,

/

Ex. Current from a lightning strike

電阻率的溫度效應

)

(

0

0

 T  T

   



Cu: 293K 1.69x10^-8

 

 







n e

m

J E

n J e E m

m eE ne

v J

m eE

a v

m eE

m F

a

d

d

2

2

) ,

(

,

/ ,

/ /





















The effect of temperature

電阻的微觀意義

eff d

eff

v v

s m

v

) 10

(

/ 10

6 . 1

13

6







 

n e

m



nm v

s

eff

40

10 5

.

2















6-3

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

R E  J

 

I-V curves

conductor pn junction diode

6-4 Semiconductors

半導體

電阻率的溫度效應：

導體與半導體的差異

 

n e

m



Superconductors

超導體

More Maglev - magnetic levitation

http://web.mit.edu/physics/hudson/ResearchBackground.htm

Maglev、MRI and Tevatron

Power line and motor

BCS Theory-The Cooper pairs

http://www.chm.bris.ac.uk/webprojects2000/igrant/hightctheory.html