Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
If a 25 mH inductor drops 50 V while operating at 400 Hz, what is XL?
1)
A)
62.8 k
B)
628
C)
6.28 k
D)
62.8
2)
Determination of an inductor’s value can be had by what method(s)?
2)
A)
Use an inductance meter.
B)
Connect the inductor in series with a known value of resistance, apply a square wave of a
known voltage value, then use the time constant formula.
C)
Apply a signal of a known frequency and voltage, then use Ohm’s law and the inductive
reactance formula.
D)
any of the above
3)
What is the total inductance of a 40 mH inductor and a 24 mH inductor connected in parallel?
3)
A)
15 mH
B)
64 mH
C)
32 mH
D)
150 mH
4)
Stray capacitance for a coil becomes a problem:
4)
A)
with low frequencies.
B)
at resonant frequencies.
C)
with high frequencies.
D)
with ac circuits.
5)
What is the reactance of a 100 µH inductor operating at 100 kHz?
5)
A)
62.8
B)
62.8 k
C)
6.28
D)
infinite
6)
What is the total inductance of a 14 mH, 22 mH and 45 mH inductor connected in series?
6)
A)
81 mH
B)
20 mH
C)
7.2 mH
D)
81 µH
7)
What is the inductive reactance of a 0.2 mH inductor operating at 1 kHz?
7)
A)
1.26 k
B)
126
C)
126 k
D)
1.26
8)
A 0.33 mH inductance is smaller than a ________.
8)
A)
0.0005 H inductance
B)
330 pH inductance
C)
0.05 mH inductance
D)
33 pH inductance
9)
If an inductor has an ac current flowing through it, the magnetic field is ________.
9)
A)
steady
B)
moving from south to north
C)
collapsed
D)
constantly changing
10)
What is the total inductance of a 25 mH inductor connected in parallel with a 100 mH inductor?
10)
A)
20 mH
B)
less than 20 mH
C)
more than 125 mH
D)
125 mH
11)
The quality factor of a coil or inductor is calculated by:
11)
A)
QL=1
2 fL
B)
QL=L
R
C)
QL= 2 fL.
D)
QL= 2 fL/RW.
12)
The time constant for an inductor for each time period:
12)
A)
is a constant value.
B)
corresponds to a 63% of the increase in value.
C)
corresponds to a 37% of the decrease in value.
D)
all of these.
13)
An 0.05 µH inductance is larger than a ________.
13)
A)
0.00005 H inductance
B)
0.0000005 H inductance
C)
0.000005 H inductance
D)
0.000000008 H inductance
14)
Connecting a ________ inductor in ________ with a 70 mH inductor produces a 100 mH inductance.
14)
A)
233 mH, parallel
B)
30 mH, parallel
C)
233 mH, series
D)
30 mH, series
15)
If an inductor carries 150 mADC of current when connected across a 65 VDC source, what is its
resistance?
15)
A)
30
B)
26.7
C)
65
D)
433
16)
Do iron–core inductors or air–core inductors generally have the larger inductance?
16)
A)
neither; iron–core inductors and air–core inductors have the same inductance
B)
iron core
C)
air core
D)
There is no way to tell.
17)
In an inductive circuit, the ________ lags the ________.
17)
A)
voltage, reactance
B)
current, resistance
C)
voltage, resistance
D)
current, voltage
18)
In an inductive AC circuit, the phase relationship between the voltage and the current is such that
the:
18)
A)
voltage is lagging the current.
B)
voltage is 360 degrees out of phase with voltage.
C)
current is lagging the voltage.
D)
current is 180 degrees out of phase with voltage.
19)
It has been determined that the source of audible noise for a radio is du to the power supply
voltage. How can an inductor be configured to eliminate this noise?
19)
A)
Connect the inductor in parallel with the radio.
B)
An inductor will not affect the noise.
C)
Connect the inductor in series with the radio power wire.
D)
both B and C
20)
If a 50 mH inductor operates at 22 kHz, XL equals ________.
20)
A)
500
B)
6912
C)
1100
D)
113
21)
What is the inductance of a 20 mH inductor connected in parallel with a 50 mH inductor?
21)
A)
14.3 mH
B)
50 mH
C)
20 mH
D)
70 mH
22)
When inductors are connected in parallel, their total inductance acts like:
22)
A)
resistance connected in series.
B)
resistance connected in series–parallel.
C)
resistance connected in parallel.
D)
all of these.
C
23)
What is the inductive reactance of an inductor that drops 12 VRMS and carries 50 mARMS?
23)
A)
6
B)
240
C)
60
D)
600
B
24)
What is the maximum current in a 12 mH inductor if it is connected in series with a 10 k resistor
and a 15 VDC source?
24)
A)
6.32 mA
B)
1.5 mA
C)
1.2 mA
D)
2.2 mA
B
25)
The ripple voltage as measured at the output of a power supply has increased. Which of the
following could be the problem?
25)
A)
partial shorting of the windings of the filtering coil
B)
load resistance has dropped
C)
resistance of the coil has decreased
D)
either A or B
D
A
Figure 11–1
26)
What is the total inductance in Figure 11–1?
26)
A)
12.7 mH
B)
95 mH
C)
225 mH
D)
15.8 mH
27)
What is the total inductance of four 10 mH inductors connected in series?
27)
A)
40 mH
B)
250 mH
C)
2.5 mH
D)
40,000 µH
28)
How many time constants will it take to completely build a magnetic field around an inductor?
28)
A)
1
B)
2
C)
3
D)
4
E)
5
29)
If two inductors are connected in a series AC circuit, which inductor drops more voltage?
29)
A)
It depends upon the source voltage.
B)
the smaller inductance
C)
It depends upon the frequency.
D)
the larger inductance
30)
If a 1 mH, 3.3 mH, and 0.1 mH inductor are connected in parallel, LT equals ________.
30)
A)
4.4 mH
B)
less than 0.1 mH
C)
greater than 3.3 mH
D)
5.3 mH
31)
What is the total inductance if a 50 mH inductor is connected in series with a 15 mH inductor?
31)
A)
15 mH
B)
50 mH
C)
65 mH
D)
11.5 mH
32)
Reactive power (Pr) in an inductor is defined as the rate at which an inductor stores or returns
energy and is measured in:
32)
A)
volts per time constant.
B)
volt–ampere reactive.
C)
watts reactive.
D)
current per time constant.
33)
What is the inductive reactance of a 150 mH inductor operating at 10 kHz?
33)
A)
9420
B)
6280
C)
1500
D)
8450
Figure 11–1
34)
How much current flows in the circuit in Figure 11–1 if connected to a 12 VPP, 2 kHz source?
34)
A)
4.77 mAp–p
B)
126 mAp–p
C)
10.1 mAp–p
D)
60.5 mAp–p
35)
Inductors ________.
35)
A)
pass direct current
B)
have a high resistance to direct current
C)
have high reactance to direct current
D)
block direct current
A
36)
What is one time constant for a 10 mH inductor connected in series with a 47 k resistor?
36)
A)
470 S
B)
0.213 µS
C)
213 µS
D)
470 mS
B
37)
How many time constants will it take to completely collapse an inductor‘s magnetic field?
37)
A)
5
B)
3
C)
1
D)
4
A
C
38)
What is the time constant for a 50 mH inductor and 5 k resistor connected in series?
38)
A)
10 µs
B)
10 ms
C)
100 s
D)
250 s
39)
If two 2.5 mH inductors are connected in series with a 4.7 k resistor and the source voltage is 100
VDC, what is the circuit’s maximum current?
39)
A)
63.2 mA
B)
1.1 mA
C)
7.9 mA
D)
21.3 mA
40)
If an inductor carries 100 mADC of current when connected across a 30 VDC source, then what is
its resistance?
40)
A)
30
B)
0
C)
300
D)
60
41)
If a 27 m H inductor has a reactance of 5.5 k, the frequency equals ________.
41)
A)
3.24 kHz
B)
32.4 kHz
C)
324 Hz
D)
932 Hz
42)
If an inductor, resistor and switch are connected in series to a 12 V battery, what is the magnitude
of the inductor’s voltage at the instant that the switch is closed?
42)
A)
12 V
B)
6 V
C)
4 V
D)
0 V
43)
The time constant of an inductor is:
43)
A)
inversely proportional to the resistance in the circuit.
B)
directly proportional to the inductance in the circuit.
C)
the time required for voltage or current to increase to 63% or to decrease to 37%.
D)
all of these.
44)
What is the reactance of an inductor that carries 1.25 mAP and drops 25 VP at 100 Hz?
44)
A)
15.7 k
B)
3.13 k
C)
20 k
D)
31.3
45)
Connecting a ________ inductor in ________ with a 100 m H inductor produces a 65 m H
inductance.
45)
A)
186 mH, parallel
B)
35 mH, parallel
C)
35 mH, series
D)
186 mH, series
46)
If a 15 µH inductor has a 2.2 K reactance, the frequency equals ________.
46)
A)
23.3 kHz
B)
4.28 MHz
C)
23.3 MHz
D)
4.28 kHz
47)
The most commonplace use for inductors in electronics:
47)
A)
blocks AC voltages.
B)
passes DC voltages.
C)
passes AC voltages.
D)
blocks DC voltages.
48)
Which type of inductor core material is likely to produce the least inductance?
48)
A)
ferrite
B)
air
C)
iron
49)
When inductors are connected in series, their total inductance acts like:
49)
A)
resistance connected in series.
B)
resistance connected in series–parallel.
C)
resistance connected in parallel.
D)
all of these.
50)
If a 50 mH inductor is in series with a 50 k resistor across a 50 VDC source, what is the maximum
current that will flow in the circuit?
50)
A)
10 mA
B)
1 mA
C)
100 µA
D)
1 µA
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
51)
The total inductance of two parallel inductors equals the sum of their inductance values.
51)
52)
The voltage leads the current in an inductive circuit.
52)
53)
The voltage and current are in phase in an inductive circuit.
53)
54)
Inductive reactance decreases as frequency increases.
54)
55)
Inductors in series or parallel combine just like resistors in series or parallel.
55)
56)
When a DC voltage is first applied to an inductor, the initial circuit current is zero.
56)
57)
An inductor is placed in series with the load for power supply filtration.
57)
58)
If an inductor is placed in an ac circuit, the ac voltage across the inductor leads the ac current
through it.
58)
59)
An inductor passes direct current and opposes alternating current.
59)
60)
An iron–core inductor is used in low frequency applications.
60)
61)
The energy stored in an inductor’s electromagnetic field is produced by the inductor’s current.
61)
62)
The quality factor for an inductor becomes more apparent at higher frequencies.
62)
63)
The energy stored in an inductor’s electromagnetic field is produced by the resistance of the
inductor’s winding.
63)
64)
True power for an inductor is measured in VAR rather than watts.
64)
Answer Key
Testname: C11
13
Answer Key
Testname: C11
14