Coulomb’s Law - University of Delaware
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Transcript Coulomb’s Law - University of Delaware
vC VC sin t
Capacitor Load
qC CvC
dqC
iC
CV cos t
dt
V
iC C sin t 90 I C sin t 90
1
C
1
X
C
The capacitive reactance of a capacitor
C
VC
I
Generalized Ohm’s law: C
Notice Ic and VC are amplitudes
XC
ICE
vL VL sin t
Inductive Load
vL L
diL
dt
VL
VL
sin
dt
cos t
L
L
V
iL L sin t 90 I L sin t 90
L
iL
The Inductive reactance of a inductive X L L
Generalized Ohm’s law: I L VL
XL
Notice IL and VL are amplitudes
ELI
The series RLC circuit
m sin d t
1. Same current through R, L, C
i I sin d t
Same frequency as in the source
I
i
vR
VR
t-
VL
vC
VC
2. Consider VR, VC, VL
VR iR IR sin d t
I
vC VC sin d t , VC IX C
2
d C
vL VL sin d t , VL IX L d LI
2
vR vC vL
The series RLC circuit: Continuous
vR vC vL
Values at t.
This relation has to be maintained
as phosors are rotating
m VR VL VC
General rules:
1. KVL and KCL still hold, but
values at the same t have to
be used, i.e. vertical
components in phasor
diagram.
2. Vectors operation for
Amplitude
v
V
The series RLC circuit: Continuous
=IZ
m VR VL VC
m
I
2
VL VC
VR
2
X L X C
R2
2
=IR
=I(XL-XC)
2
1
2
I L
R
C
I
m
R
C
2
L 1
tan
L 1C
R
2
m
Z
Z is the impedance of the circuit
X L XC
R
Examples
33-43P. A coil of inductance 88 mH
and unknown resistance and a 0.94 mF
are connected in series with an
alternating emf of frequency 930 Hz.
If the phase constant between the
applied voltage and current is 75,
what is the resistance of the coil.
f=930 Hz
d=2f
=IZ
=IR
=I(XL-XC)
=IZ
RLC Resonance
tan
L 1C
R
=IR
X L XC
R
XL>XC: inductive loading
=I(XL-XC)
XL=XC: Resonance
XC>XL: Capacitive loading
RLC Resonance: Cont
tan
L 1C
R
X L XC
d L 1 C
d
d
I max
1
LC
m
R
X L XC
R
I
m
L 1C R
2
2
Conditions at Resonance
I
=IZ
m
X L X C 2 R 2
=IR
m
L 1C R
2
2
• I is a maximum
=I(XL-XC)
• Z is at minimum; Z=R; Z is purely resistive
• XL=XC; inductive reactance cancels capacitive reactance;
net reactance is zero
• The phase angle is zero; the current is perfectly in phase
with applied emf; the tangent of the phase angle is zero.
• The driven frequency is identical to the natural frequency.
• The power factor is unity