7 電路
7.1 直流電路 7.2 串聯電阻 7.3 並聯電阻 7.4 交流電路
7.5 虛擬電路實驗
Outline
7.1
直流電路•Direct Current Circuit
•A bimetallic strip flasher
•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.1 簡單直流電路內之電位(電壓)
升降
a a
V iR V
iR
E E
克希荷夫 Kirchhoff 迴 路定理
Ex.2
The Ammeter and the VoltmeterA single-loop circuit
• Follow Example 26.3, using Figure 26.10 below.
Power distribution systems
• Follow the text discussion using Figure 26.24 below.
Household wiring
• Figure 26.26 at the right shows why it is safer to use a three-prong plug for
electrical appliances.
Figure 26.25
fuse
Circuit breaker
Neuromyography
Ex.3 RC電路
電阻-電容電路
Ex.3
(cont) Charging a
Capacitor0 ,
1 ( )
( )
( ) ( )
q dq
iR i
C dt
dq q dq q
R dt C dt RC R
dq q
dt R RC RC q C
dq dt d q C dt
q C RC q C RC
E
E E
E E
E
E E
Ex.3 (cont)
const
const
( )
( )
ln( ) Const.
What is C ?
t RC
t t
RC RC
d q C dt
q C RC
q C t
RC
q C e
q C e e C e
EE
E E
E
Ex.3 (Initial Condition)
0 0
/
/
( ) '
0 ' '
( )
( ) (1 )
( )
t RC
t RC
t RC t RC
t RC
q t C C e
C C e C C
q t C C e
q t C e
i dq e
dt R
E
E E
E E
E E
Ex.3
(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。
( ) (1 RC RC/ ) 0.63
q RC CE e CE
10106
10 6
10s F
RC
e-1
UnFigure Page 866
7.2
Resistance in series
n
j
j eq
eq
R R
R R
R i R
iR iR
iR
1
3 2
1
3 2
1
0
E E
E
7.3 Resistors in parallel
3 2
1
3 2
1 3
2 1
3 3
2 2
1 1
1 1
1 1
1 ) 1
( 1 , ,
R R
R R
i R
R R
i R i
i i
i R i R
i R
eq eq
E
E
E E
E
Multiloop Circuits
The Junction rule: 流入接點之電流必等 於流出者
(Kirchhoff’s junction/current rule)
2 3
1
i i
i
loop left
3 0
3 1
1
1 i R i R E
loop right
2 0
2 2
3
3
i R i R E
loop big
2 0
2 2 1
1
1 E
E i R i R
解System of equations (聯 立方程組)
Ex.4 What are the currents?
0 0
2 2
2 1
3 2
1 3
2 2
2 1
1 1
1 1
2 1
3
R i
R i
R i
R i
R i R
i
i i
i
E E
E
E
解聯立方程組
pivot equation
Forward Elimination and Back substitution
pivot equation
upper triangle
高斯消去法
The torpedo ray
Ex.5 The electric eel
The Equivalent circuit
A 10
6 . 6 140
/
A 93 .
0 0
93 .
1 8 1 140
1
1250 5000
V 750 5000
3 140
1
i i
i iR
iR
R R R
R
r R
row
eq w
row
eq j j row
eq
ep row
ep row
E
E E
The current
Rw=800Ω 0.15V
0.25Ω
7.4
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
rms rmsV V I
V I I
P
2 2 2
1 0 0
0 0
R I
Vrms rms
R R V
I V
I
P rms rms rms rms
2
2
Ex.5 72W 音箱
V V
Vrms V 24 2
34 2
0
3.0
0 . 8
24V R
Irms Vrms
W V
I
P rms rms 72
Ex.6 A practical example
Quebec MontrealM W 0
. 55 )
1000 /
22 . 0 (
) A 500 (
M W 220
) 1000
/ 22
. 0 (
) A 1000 (
368M W V)(500A)
10 35
. 7 (
2 2
2 ,
2 2
1 ,
5
km m
R I
P
km m
R I
P
I P
av av
av E