전류와전기회로 -...
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전류와 전기회로
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Chapter 26 Current and Resistance
New concepts in Chap. 26:
Electric current ( symbol i )
Electric current density vector (symbol )
Drift speed (유동속력) (symbol vd )
Resistance (전기저항;symbol R )
and resistivity (비저항;symbol ρ ) of a conductor
Ohmic and non-Ohmic conductors
J
We will also cover following topics: Ohm’s law Power(일률,전력) in electric circuits
Up to Chap. 25 : Electrostatics (정전기학)
+ -
i
V
conductor
P. 857
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p. 858Electric Current ( symbol i )
등전위체
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i
+q
conductor
v
i
-q
conductor
v
Ele
ctri
SI
c curren
Unit:
t :
C/s " mpereA "
dqit
id
p. 858Consider a ( ) connected to conducto a battr ery:도체
Direction of electric current :
+ +
+ +
+
+
i
-
-
-
-
-
-
i
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i
- q
conductor
v A
J
Magnitude
Direction of : the same as that of the curr
]
en
)
t
전류밀도 J
iJA
J
Current density( :
2SI unit for A/mJ: [i
+ q
conductor
v A
J
1 2
Current density : a Electric current : a At a point a, Conservation of Char : " @ a"
(Note that we h
ge
av
v
e used vector additi
ectorscal
not o )
ar
n.oi i i
Ji
p. 860
if constant.
If is not constant
,
i JA J
iJ J dA
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When a current flows through a conductor, the charges move with a constant drift speed . dv
Drift speed, 유동속력
In vector form,
dJ nev(26 - 5)
Random MoDrift Mot superimposed on the of the charged parti
tiocl
n nioes.
F
dv
Consider a conductor of cross sectional area : The total charge within a length ,
* moves through area in a time :
.
d
Aq L q Ne nAL e
Lq A
q L
v
nA
t
it
eL
/
d
ddn nv e Aiv eA J
Av
A dnev
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보기문제 p. 862
원통형 도선에 흐르는 전류
2( ) b J ar
2( / 2)
/ 2
4
15
2
32
RR r R
RdA ri J dA J ar
a
d
R
r
2 dA r dr
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+ -
i
V
Under a voltage across a conductor,
V [ ] "Ohm" (symbol
)A
VRi
R
V
SI Unit for :
R
p. 864
"Resistor" : A conductor whose function is to provide a specified resistance.
저항(체)
Why not use the symbol "O" instead of " " ? Suppose we had a 1000 resistor.
We would then write: 1000 O which can easily be mistakenly read as 10 0 .
00
Q :A :
)Resistanc (e 전기저항
R
V
conductor
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E
+ -
i
V
E
unlike the electrostat
Re
ic case.
of the conductor, sistivit
0)
y
비저항
insideEEJ
Resistivity ( :
Electric field inside the conductor: & Current density: .
/ /
V L
V i
V A ARi A i
E JL
L L
AE LRJ A
LRA
E J
J E
2
V/m V m mA/m
Electrical conduc
In vector form,
tivity , 1
A
E J
J E
SI unit for :
p. 866
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초전도체
p. 867
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Ohm의 법칙
JERiV
또는
p. 868
Ohm's law Ohmic con ' ' is, in reality, a definition of ( the conductors defi that
ducto obey
rs One hmd as 's law)
Note :
" "non - Ohmic" "Ohmic
Rectification (정류작용)
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전기에너지
공급율
에너지 소모율
전기 퍼텐셜 에너지 감소
다른 형태의 에너지로 변환
dq
p. 871
dq idt
>a bV V
V A W " " ( Wsymbott l ).aP SI unit for :
전기회로의 일률(=전력;Power)
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기전력 장치
기전력장치 (직류회로) p. 886
( )
dWdq
기전력 의정의
전지, 발전기, 태양전지, 연료전지, 열전대 (thermocouple) 등
단위는 V (volt)
연료전지(fuel cell): 외부에서 연료(수소 또는 메타놀)와 산소를
계속 공급해서 연료가 산화하면서 계속 전기 에너지를 공급열전대 (thermocouple): ??
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직류회로:
B A( 인 경우)
전기저항
기전력 장치
p. 887
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0iR
회로에 흐르는 전류와 전위차 계산하기: Kirchhoff 회로 방정식
P =i 2R 발생된 열에너지= i2R dt(in the resistor during dt)
p. 888Kirchhoff의회로규칙1. Kirchhoff의고리규칙(전압규칙)
-- 고리회로를따라퍼텐셜차이를더해나가면그결과는 0 이다.(에너지보존원리)
dq =i dt
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2. Kirchhoff의접점규칙 (전류규칙)-- 하나의접점으로들어오는전류의합은나가는전류의합과같다.
(전하보존원리)
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2
mf
( ) r
R RR r r
iP
P iV iR r
ir i riP
기전력 장치가 저항체에전달하는 ‘유효’ 일률
p. 889
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p. 890
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8.0 V b aV V
0.0 V 8.0 V
a
b
VV
0.0 V 8.0 V
b
a
VV
회로의 접지 접지된 지점의 퍼텐셜을 0으로 정의
i=2A
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p. 895
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병렬과 직렬이 섞인 회로 p. 897
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보기문제 p. 901
1 2 3For a junction , 0 a i i i
1 1 1 1 1 1 2 2 2For the left loop, ) 0 (i R i R i i R
2 1 2 2 1 1 2 2 2For the right loop ( ) 0, i R i R i i R
1
2
3
0.50 A 0.25 A
0.2
5 A
iii
2 3 2
2 3 2 6 ( 0.25)(4) 5 [V]ba a
b a
b
V i R ViV V V R
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p. 901
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:
p. 902
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1 1
(1
1 ln( - ) ln( )
- 1 n
- )
l
tRRC C
t
q c c tRC
q c tc
q c e
RCq c e
c
,
0
: 0
0
고리규칙 dqidt
dq q dq qRdt C R dt R
q
C
iRC
1 = ( - )
1 = ( - )
dq q q cdt RC R RC
dq q c dtRC
- 1=dq dt
q c RC
0 0
0 0
' 1 = ''-
1 ln( '- ) | ' |
q t
q t
dq dtq c RC
q c tRC
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2000 , 1 F , =10VR C m e= W = 2.718e
RC회로의 특성시간
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