Ch 19. DC Circuits

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7 Οκτ 2013 (πριν από 3 χρόνια και 6 μήνες)

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Ch 19. DC Circuits
Liu UCD Phy1B 2012
I. EMF and Terminal Volta
g
e
g
Electric circuit needs battery or generator to produce current –
thlldflttif(f)
th
ese are ca
ll
e
d
sources o
f
e
l
ec
t
romo
ti
ve
f
orce
(
em
f)
.
Battery is a nearly constant voltage source, but does have a small
internalresistance
r
whichreducestheactualvoltagefromthe
internal

resistance

r
,
which

reduces

the

actual

voltage

from

the

ideal emf:
Terminalvoltage
Terminal

voltage
Liu UCD Phy1B 2012
IIResistorsinSeries
II
.
Resistors

in

Series
StI
EiltitR
S
ame curren
t

I
V=V1+V2+V3=IR1+IR2+IR3
E
qu
i
va
l
en
t
res
i
s
t
ance
R
eq:
V=IRe
q
Liu UCD Phy1B 2012
q
Req= R1+R2+R3
III. Resistors in Parallel
EquivalentresistanceR
I= I
1+I2+I3
VthhR
Equivalent

resistance

R
eq:
I=V/Req
V/R
V/R
V/R
V/R
V

th
e same across eac
h

R
I1=V/R1; I2=V/R2; I3=V/R3
V/R
eq=
V/R
1+
V/R
2+
V/R
3
1/Req= 1/R1+1/R2+1/R
3
Siltilll
R
R
R
/(R
+R
)
Liu UCD Phy1B 2012
S
pec
i
a
l
case:
t
wo
i
n para
ll
e
l

R
eq=
R
1
R
2
/(R
1
+R
2
)
Examples
Examples
R1=100R2=300

R
?
R

?
P
1
㼠?
2
㼠?
瑯瑡t㼠
I
1
㼠?
2
㼠?
瑯瑡t㼠
V


?
V
1
?

V
2
?

V
瑯瑡t
?

䱩甠啃䐠偨礱䈠㈰ㄲ
Examples
Examples
RA=RC=100, RB=300,
V=35V
S closed, Req? IA, IB, IC?
V
A, VB, VC?
S open, Req? IA, IB, IC?
V
A
,
V
B
,
V
C
?
A
,
B
,
C
Liu UCD Phy1B 2012
IVComparison
IV
.
Comparison
SeriesParallel
I sameV same
V add upI add up
Req=R1+R2
Req=R1R2/(R1+R2)
Largerthaneitherone
Smallerthaneitherone
Liu UCD Phy1B 2012
Larger

than

either

one
Smaller

than

either

one
ComplexCircuits
Complex

Circuits
Draw equivalent circuits
Siliftbt
Liu UCD Phy1B 2012
Si
mp
lif
y s
t
ep
b
y s
t
ep
MoreExample
More

Example
Liu UCD Phy1B 2012
ElectricalHazard
Electrical

Hazard
Liu UCD Phy1B 2012