# Chapter 33. AC Circuits.

Electronics - Devices

Oct 5, 2013 (4 years and 9 months ago)

171 views

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
-

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

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