lecture5 (chap 5)

7/28/2019 Lecture5 (Chap 5)

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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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CXIV rmsrms fC

XC2

1

capacitivereactance


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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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A0236.01060

V0.25rmsrms

CX

VI

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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For a purely resistive circuit,

the current and voltage arein phase.


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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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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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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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23.3Circuits 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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22 CL XXRZ

222 )( CLro VVVV

C C C


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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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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.



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THE SEMICONDUCTOR DIODE



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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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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.



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A half-wave rectifier.



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SOLAR CELLS



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TRANSISTORS

A bipolar junction transistor can

be used to amplify a smaller

voltage into a larger one.



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23.5 Semico ndu ctor Devices


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lecture5 (chap 5)

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