Chapter 33. AC Circuits.

piquantdistractedElectronics - Devices

Oct 5, 2013 (3 years and 11 months ago)

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Alternating Current (AC)
Circuits


AC Voltages and Phasors


Resistors, Inductors and Capacitors in AC
Circuits


RLC Circuits


Power and Resonance

AC Sources and Phasors

Consider a sinusoidal voltage source:

This source can be represented graphically as a vector called a
phasor
:


t

time

T

V
max

-
V
max

V
max

V(t)

b

c

b

c

d

e

d

a,e

a

Great web page:
http://www.phys.unsw.edu.au/%7Ejw/AC.html

Resistors in AC Circuits

Since both have the
same arguments in
the sine term,
i
R

and

v
R

are in line, they
are
in phase
.

Root Mean Square (RMS) Current
and Voltage

Announcements



Cell phones on silent


Check mid
-
term grades.

Inductors in AC Circuits

Inductive
Reactance

For a sinusoidal voltage,
the current in the inductor
always
lags

the voltage
across it by 90
°
.

Inductors in AC Circuits


Filter for woofer


Low frequencies
pass through


High frequencies
get blocked.

V
R


Frequency

Woofer

Capacitors in AC Circuits

Capacitive
Reactance

For a sinusoidal voltage,
the current in the
capacitor always
leads

the voltage across it by
90
°
.

Inductors in AC Circuits


Filter for tweeter


High frequencies
pass through


Low frequencies
get blocked.

V
R


Frequency

Tweeters

RLC Series Circuit

Using Phasors in a RLC Circuit

Impedance

R = 425
W

L = 1.25 H

C = 3.5
m
F



= 377 s
-
1


V
max

= 150 V

Example 33.5

Power in an AC Circuit

For a purely resistive load,

=0

No power loss occurs in
an ideal capacitor or
inductor.

Resonance in Series RLC Circuits

A circuit is in resonance when its current is maximum.

I
rms
=max

when
X
L
-
X
C
=0

Resonance Frequency

Tuner for radio!

www.barlowwadley.it

Inductor

Variable
Capacitors