terry (ect328) – homework 32 – Turner – (59130)
1
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printout
should
have
10
questions.
Multiplechoice questions may continue on
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before answering.
001
(part 1 of 3) 10.0 points
In an
LR
circuit, a 174 V(
rms
), 78 Hz source
is in series with a 21 mH inductor and a 10
Ω
resistor.
What is the maximum
rms
current?
Correct answer: 12
.
1254 A.
Explanation:
Let :
f
= 78 Hz
,
L
= 0
.
021 H
,
R
= 10
Ω
,
and
V
rms
= 174 V
.
The inductive reactance is
X
L
=
ω
L
= 2
π
f L
= 2
π
(78 Hz) (0
.
021 H)
= 10
.
2919
Ω
.
The impedance of an
RL
circuit is the same
as that of an
RLC
circuit, but without the
capacitive reactance. Namely
Z
=
R
2
+
X
2
L
=
(10
Ω
)
2
+ (10
.
2919
Ω
)
2
= 14
.
35
Ω
.
The
rms
current is
I
rms
=
V
rms
Z
=
174 V
14
.
35
Ω
=
12
.
1254 A
.
002
(part 2 of 3) 10.0 points
What is the power factor?
Correct answer: 0
.
696864.
Explanation:
The phase angle in an
RL
circuit is the
same as that of an
RLC
circuit, but without
the capacitive reactance. Namely
φ
= tan

1
X
L
R
= tan

1
10
.
2919
Ω
10
Ω
= 45
.
824
◦
So, the power factor is
cos
φ
= cos(45
.
824
◦
) =
0
.
696864
.
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 Spring '10
 Turner
 Inductance, RLC, Correct Answer, Inductor, RL circuit

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