DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
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T F 1.
Resonant frequency of a circuit occurs when the inductive reactance is equal to the
capacitive reactance.
T F 2.
In a series resonant circuit, current is maximum and impedance is minimum at
resonance.
T F 3.
In a series RLC circuit, a
t above resonance the circuit is more capacitive than it is
inductive.
T F 4.
A parallel tuned circuit can be used to couple energy from one circuit to another.
T F 5.
By increasing the resistance of a coil you can increase the Q of the coil at res
onance.
T F 6.
Parallel LC circuits that produce an AC signal at a desired frequency are called "tank
circuits."
T F 7.
In a parallel resonant circuit, impedance is minimum and current is maximum.
T F 8.
Parallel resonant circuits reject curre
nts at resonant frequency.
T F 9.
Series resonant circuits pass currents at resonant frequency.
T F 10.
The Q of a resonant circuit describes the relationship of the reactance to the
impedance.
11.
In a series RLC circuit the current can be fou
nd using
A.
I
t
= V
r
/R.
B.
I
t
= V
t
/Z.
C.
Both A and B.
D.
None of the above.
12.
True power in an RLC circuit equals I squared times R when
A.
the circuit is at resonance.
B.
it is a series circuit.
C.
it is a parallel circui
t.
D.
All of the above.
13.
Apparent power in an RLC circuit is equal to total voltage times total current when
A.
the circuit is at resonance.
B.
it is a series circuit.
C.
it is a parallel circuit.
D.
All of the above.
14.
When
inductive reactance equals capacitive reactance, the circuit
A.
draws maximum current.
B.
draws minimum current.
C.
is at resonance.
D.
All of the above.
15.
At resonance the power factor is
A.
0.
B.
1.
C.
negative.
D.
No
ne of the above.
DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
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16.
The lower and upper end of the band width of a series RLC circuit is where the current has
fallen to _______________ the maximum.
A.
50%
B.
75%
C.
70.7%
D.
14.4%
17.
When a parallel circuit resonates it is said t
o
A.
flywheel
B.
oscillate
C.
Both A and B.
D.
Neither A nor B.
18.
At frequencies well above and below the resonant frequency, the series RLC circuit looks
______________ and the parallel RLC circuit looks _______________.
A.
capaci
tive, inductive
B.
inductive, capacitive
C.
like an open, like a short
D.
like a short, like an open
19.
In a low

pass filter the capacitor must be _______________ and the inductor must be
_______________.
A.
in series, in shunt
B.
i
n shunt, in series
C.
a high value, a low value
D.
a low value, a high value
20.
A band pass filter can have the tank circuit
A.
in series.
B.
in shunt.
C.
Both of the above.
D.
Neither of the above.
21.
In AC circuits with bot
h resistance and reactance, the apparent power supplied by the source
is not the _______________ power dissipated in the form of heat.
22.
Power is always ________________________ in any circuit.
23.
Power graphs are plotted at ______________________
the frequency of the applied voltage.
24.
True power in a reactive circuit is determined by finding the amount of power dissipated by
the ________________________ in the circuit.
25.
Inductive reactance can be expressed into rectangular notation by
using a
________________________ j factor.
26.
Capacitive reactance can be expressed in rectangular notation by using a
________________________ j factor.
DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
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27.
Quantities in rectangular format can easily be mathmatically _____________________ and
_____
______________, but not easily ___________________ and ____________________.
28.
Polar notation can be used to express the resultant _________________________ and
_________________________ of a circuit
29.
If the voltage across the inductor and the c
apacitor are the same in a series circuit, then the
circuit must be at _______________________________
30.
Algebraic vector analysis involves both __________________________ and
___________________________ forms to analyze vector quantities.
31.
Why
don't we use the j operator in DC circuit analysis?
__________________________________________________________________
__________________________________________________________________
32.
Why is one form used for addition and subtraction of complex nu
mbers and the other form
used for multiplication and division of complex numbers?
__________________________________________________________________
__________________________________________________________________
33.
What must be done before a final
solution can be found if there is more than one resistance,
inductive reactance or capacitive reactance in a circuit?
__________________________________________________________________
Note: Refer to Figure 21

1 for questions 34 to 40 inclusive.
34.
Using rectangular format, express the amount
of resistance and reactance for the circuit shown.
___________________________________________
35.
For the circuit shown, will the circuit be more
inductive or more capacitive?
___________________________
________________
36.
For the circuit shown, will the voltage lead or
lag the current?
_________________________________________
DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
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37.
For the circuit shown, explain what would happen if the frequency were to increase.
_____________________________
_____________________________________
__________________________________________________________________
38.
Is the circuit at resonance. If not, why?
__________________________________________________________________
__________________________________
________________________________
39.
For the circuit to be at resonance, what would have to happen to frequency?
__________________________________________________________________
40.
For the circuit, if the resistor were to short, what would happen
to current?
__________________________________________________________________
Note: Draw the indicated circuits for questions 41 to 45 inclusive.
41.
A simple series RLC circuit.
42.
A simple parallel RLC circuit.
43.
A graph illustrating insta
ntaneous power in a purely resistive AC circuit.
44.
A vector diagram illustrating apparent power, reactive power, and true power for a series RL
circuit.
45.
A vector diagram illustrating apparent power, reactive power, and true power for a series R
C
circuit.
46.
You are observing the voltage signals across an inductor and a capacitor in a series RLC
circuit and notice that they are 180 degrees out of phase. Is there anything wrong?
________________________________________________________________
___
47.
The voltage drop across an inductor and a capacitor in a series RLC circuit is the same value.
What must the circuit conditions be for this to be true?
__________________________________________________________________
48.
If capacitive reac
tance is twice that of inductive reactance, what can be said about circuit
current in a series RLC circuit?
__________________________________________________________________
49.
Why isn't apparent power the same as true power?
_______________________
___________________________________________
__________________________________________________________________
__________________________________________________________________
50.
What is wrong if the voltage drop across the resistor in a series RLC c
ircuit reads the same as
applied voltage?
__________________________________________________________________
__________________________________________________________________
DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
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Answers for Questions 21a
1
T
2
T
3
F
4
T
5
F
6
T
7
F
8
T
9
T
10
F
11
C
1
2
D
13
D
14
C
15
B
16
C
17
C
18
C
19
B
20
C
21
true, or real, or resistive
22
p
ositive
23
twice
24
resistance
25
positive
26
negative
27
added and subtracted, multiplied and divided
28
impedance and phase angle
29
resonance
30
rectangular and polar
DC / AC Introduction

Section 21

Series and Parallel RLC Circuits
Monday Novembe
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31
There are no reactance quantities in DC circuits.
32
Rectangular are individual quantities and can be added or subtracted. Polar are resultant
quantities and can be multiplied or divided.
33
They must be combined first.
34
200

j 250
.
35
The circuit is more capacitive at this particular frequency.
36
Voltage will lag the current because the circuit is capacitive.
37
Capacitive reactance would decrease and inductive reactance would increase.
38
No. Capacitive reactance is grea
ter than inductive reactance.
39
Frequency would have to increase.
40
Current would increase if any component shorts.
41
Similar to Figure number 21

7 on page 687.
42
Similar to Figure number 21

11 on page 692.
43
Similar to Figure number 21

13 on page 695
.
44
Similar to Figure number 21

18a on page 699.
45
Similar to Figure number 21

18b on page 699.
46
No, this is normal.
47
The circuit is at resonance.
48
Current will lead the voltage.
49
Reactive components return power to the circuit and create a phase
angle between current and
voltage. (V and I are not in phase.)
50
The resistor is open, or X
L
and X
C
are equal in value, thus
canceling
each other.
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