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Alternating Current Circuit
Capacitors and Capacitive Reactance
Inductors and Inductive Reactance
Circuit containing Resistance, Capacitance and
Inductance
Resonance in Electric Circuit
Semiconductor Devices
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23.1Capacitors and Capacit iv e Reactance
The resistance in a purely resistive circuit has the same value
at all frequencies.
RIV rmsrms
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23.1Capacitors and Capacit iv e Reactance
CXIV rmsrms fC
XC2
1
capacitivereactance
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23.1Capacitors and Capacit iv e Reactance
Examp le 1A Capacitor in an AC Circuit
The capacitance is 1.50F and the rmsvoltage is 25.0 V. What is the rms current
when the frequency is (a) 100 Hz and
(b) 5000 Hz?
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23.1Capacitors and Capacit iv e Reactance
A0236.01060
V0.25rmsrms
CX
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1060
F1050.1Hz1002
1
2
16 fC
XC(a)
(b)
2.21
F1050.1Hz50002
1
2
16 fC
XC
A18.121.2
V0.25rmsrms
CX
VI
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23.1Capacitors and Capacit iv e Reactance
For a purely resistive circuit,
the current and voltage arein phase.
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23.1Capacitors and Capacit iv e Reactance
The current in a capacitor leads
the voltage across the capacitor
by a phase angle of 90 degrees.
The average power us ed by a capacitor in an ac circ uit is zero.
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23.1Capacitors and Capacit iv e Reactance
In the phasormodel, the voltageand current are represented by
rotating arrows (called phasors).
These phasors rotate at a frequency f.
The vertical component of the phasor
is the instantaneous value of the current
or voltage.
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23.2Induc tors and Induct ive Reactance
LXIV rmsrms
inductive
reactance
LfXL 2
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23.2Induc tors and Induct ive Reactance
The current lagsbehind thevoltage by a phase angle of
90 degrees.
The average power used by an inducto r in an ac circuit is zero.
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23.2Induc tors and Induct ive Reactance
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23.3Circuits Con taining Resistanc e, Capacitance, and Indu ctanc e
In a series RLC circuit, the total opposition to the flow is
called the impedance.
ZIV rmsrms 22 CL XXRZ
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23.3Circuits Con taining Resistanc e, Capacitance, and Indu ctanc e
22 CL XXRZ
222 )( CLro VVVV
C C C
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23.3Circuits Con taining Resistanc e, Capacitance, and Indu ctanc e
R
XX
V
VV CL
R
CL
tan
phase angle between
current and total voltage
coscos rmsrms2
rm s VIZIP
power factor
23 4 R i El t i Ci i t
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23.4Resonance in Electr ic Circui ts
Resonanceoccurs when the frequency of a vibrating force exactly
matches a natural (resonant) frequency of the object to which the
force is applied.
The oscillation of a mass on a spring is analogous to the oscillation of
the electric and magnetic fields that occur, respectively, in a capacitor
and an inductor.
23 4 R i El t i Ci i t
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23.4Resonance in Electr ic Circui ts
22
rmsrms
212 fCfLR
VI
22
212 fCfLRZ
Reson ant frequencyLC
fo2
1
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Exercise 1
An ac generator supplies a peak (not rms) voltage of 150
V at 60.0 Hz. The generator is connected in series with
a 35-mH inductor, a 45-F capacitor and an 85-W
resistor.
a) Determine the rms voltage of the generator.
110 V
b) What is the capacitive reactance for this circuit?
59 ohm
c) What is the inductive reactance for this circuit?
13 ohm
d) What is the impedance of the circuit?
97 ohm
23 5 S i d t D i
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23.5Semico ndu ctor Devices
Semiconductor devices such as diodes and transistors are widely
used in modern electronics.
23 5 Semico ndu ctor Devices
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23.5Semico ndu ctor Devices
n-TYPE AND p-TYPE SEMICONDUCTORS
The semiconducting materials (silicon and
germanium) used to make diodes and
transistors are dopedby adding small
amounts of an impurity element.
23 5 Semico ndu ctor Devices
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23.5Semico ndu ctor Devices
THE SEMICONDUCTOR DIODE
23 5 Semico ndu ctor Devices
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23.5Semico ndu ctor Devices
At the junction between the n and p materials, mobile electrons and
holes combine and create positive and negative charge layers.
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23.5Semico ndu ctor Devices
There is an appreciable current through the diode when the
diode is forward biased.
Under a reverse bias, there is almost no current through the
diode.
23 5 Semico ndu ctor Devices
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23.5Semico ndu ctor Devices
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23.5Semico ndu ctor Devices
A half-wave rectifier.
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23.5Semico ndu ctor Devices
SOLAR CELLS
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23.5Semico ndu ctor Devices
TRANSISTORS
A bipolar junction transistor can
be used to amplify a smaller
voltage into a larger one.
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23.5Semico ndu ctor Devices
23.5 Semico ndu ctor Devices
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23.5Semico ndu ctor Devices