Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
In an ideal transformer, both coils are linked by
1)
A)
all of the total magnetic flux.
B)
none of the total magnetic flux.
C)
part of the total magnetic flux.
D)
None of the above
2)
In aseries–aiding configuration of two mutual inductors
2)
A)
the magnetic flux of each coil adds to the magnetic flux of the other coil.
B)
the total inductance is larger than the sum of the two coil inductances.
C)
Both Aand B
D)
Neither Anor B
3)
In amutual inductor, both coils are linked by
3)
A)
none of the total magnetic flux.
B)
part of the total magnetic flux.
C)
all of the total magnetic flux.
D)
None of the above
4)
Astep–down transformer has aturns ratio of 20:1. The primary voltage is 1000 V. The secondary
voltage is
4)
A)
2.5 V
B)
50 V
C)
20 kV
D)
None of the above
5)
The coupling coefficient expresses the relationship between
5)
A)
the mutual inductance only.
B)
both coil inductances and the mutual inductance.
C)
both coil inductances only.
D)
None of the above
6)
Astep–down transformer has aturns ratio of 20:1. The load impedance is 100.The input
impedance on the primary side is
6)
A)
2 k
B)
40 k
C)
5
D)
None of the above
B
7)
The quantity that is equal on both sides of an ideal transformer is
7)
A)
complex power.
B)
real power.
C)
reactive power.
D)
All of the above
D
8)
The voltage induced into an inductor by atime–changing magnetic field
8)
A)
opposes achange in voltage.
B)
opposes achange in current.
C)
Both Aand B
D)
Neither Anor B
B
9)
The side of the transformer that is considered the “output” is
9)
A)
the secondary side.
B)
the primary side.
C)
Both of the above
D)
None of the above
A
B
10)
The side of the transformer that is considered the “input” is
10)
A)
the secondary side.
B)
the primary side.
C)
Both of the above
D)
None of the above
11)
The two generic classifications of coupled coils are
11)
A)
ideal transformers.
B)
mutual inductors.
C)
Both Aand B
D)
Neither Anor B
12)
The term “step–down” means that
12)
A)
the primary voltage is larger than the secondary voltage.
B)
the primary current is smaller than the secondary current.
C)
Both of the above
D)
None of the above
13)
Astep–down transformer has aturns ratio of 20:1. The primary current is 1mA. The secondary
voltage is
13)
A)
20 mA
B)
50 µA
C)
400mA
D)
None of the above
14)
The input impedance to astep–uptransformer is
14)
A)
greater than the load impedance.
B)
the same as the load impedance.
C)
smaller than the load impedance.
D)
indeterminate.
15)
The mutual inductor can be considered an ideal transformer when
15)
A)
there is complete flux linkage between both coils.
B)
coil reactances are much greater than other circuit impedances.
C)
Both Aand B
D)
Neither Anor B
16)
The ideal transformer is called “ideal” because
16)
A)
zero conductor losses are assumed.
B)
all of the magnetic flux linking both coils is assumed.
C)
zero losses in the magnetic material are assumed.
D)
All of the above
17)
Which quantities does the transformer transform from one side of the transformer to the other side
of the transformer?
17)
A)
Impedance and power
B)
Current and voltage
C)
Voltage and power
D)
None of the above
18)
Astep–down transformer has aturns ratio of 20:1. The number of turns in the primary is 10,000. The
number of turns in the secondary is
18)
A)
25
B)
500
C)
200,000
D)
None of the above
19)
The term “step–up” means that
19)
A)
the primary current is smaller than the secondary current.
B)
the primary voltage is larger than the secondary voltage.
C)
Both of the above
D)
None of the above
20)
The mutual inductance is
20)
A)
the square root of the product of the inductances of two coupled coils.
B)
the difference in the inductances of two coupled coils.
C)
the sum of the inductances of two coupled coils.
D)
the inductance between both coils of two coupled coils.
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
21)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a
(2 – j5) kload. The primary current is ________.
21)
22)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 + j20 load. The complex power in the load is ________.
22)
23)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 load. The secondary voltage is ________.
23)
24)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 + j20 load. The primary current is ________.
24)
25)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a
(2 – j5) kload. The complex power in the load is ________.
25)
26)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a
(2 – j5) kload. The secondary voltage is ________.
26)
27)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 load. The power in the load is ________.
27)
28)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 load. The primary current is ________.
28)
29)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 + j20 load. The input impedance on the primary side of the transformer is ________.
29)
30)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a 2
kload. The power in the load is ________.
30)
31)
Amutual inductor is connected to a50 load. The primary coil is 3mH, the secondary coil
is 5mH, and the mutual inductance is 2mH. The source is 20 mV (RMS) at afrequency of 3
kHz. The power in the load is ________.
31)
32)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 + j20 load. The secondary voltage is ________.
32)
33)
Amutual inductor is connected to a50 load. The primary coil is 3mH, the secondary coil
is 5mH, and the mutual inductance is 2mH. The source is 20 mV (RMS) at afrequency of 3
kHz. The secondary voltage is ________.
33)
34)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a
(2 – j5) kload. The load current is ________.
34)
35)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a 2
kload. The primary current is ________.
35)
36)
Amutual inductor is connected to a50 load. The primary coil is 3mH, the secondary coil
is 5mH, and the mutual inductance is 2mH. The source is 20 mV (RMS) at afrequency of 3
kHz. The primary current is ________.
36)
37)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 load. The load current is ________.
37)
38)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 load. The input impedance on the primary side of the transformer is ________.
38)
39)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a
(2 – j5) kload. The input impedance on the primary side of the transformer is ________.
39)
40)
Astep–down transformer with aturns ratio of 10:1 is connected to a25 V(peak) source and
a50 + j20 load. The load current is ________.
40)
41)
Amutual inductor is connected to a50 load. The primary coil is 3mH, the secondary coil
is 5mH, and the mutual inductance is 2mH. The source is 20 mV (RMS) at afrequency of 3
kHz. The input impedance on the primary side of the mutual inductor is ________.
41)
42)
Astep–uptransformer with aturns ratio of 1:10 is connected to a25 V(peak) source and a 2
kload. The secondary voltage is ________.
42)
43)
Amutual inductor is connected to a50 load. The primary coil is 3mH, the secondary coil
is 5mH, and the mutual inductance is 2mH. The source is 20 mV (RMS) at afrequency of 3
kHz. The secondary current is ________.
43)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
44)
Lenz’s Law states that the induced effect always opposes the cause of the induced effect.
44)
45)
An ideal transformer transforms power levels from one side of the transformer to the other side.
45)
46)
Power cannot transfer through atransformer because the two coils are not electrically connected by
wires.
46)
47)
The transformer transforms voltage levels from one side of the transformer to the other side.
47)
48)
Amutual inductor has partial flux linkage from one coil to the other.
48)
49)
The impedance scales by n2from one side of an ideal transformer to the other side.
49)
50)
Atime–changing magnetic field can induce a voltage into aconductor.
50)
51)
The impedance scales by n2from one side of amutual inductor to the other side.
51)
52)
Amutual inductor obeys the same assumptions as an ideal transformer.
52)
53)
An inductor opposes an instantaneous change of voltage.
53)
54)
In general, the primary side of the transformer affects the secondary side and the secondary side
affects the primary side.
54)
55)
The voltage and current relationships in amutual inductor are characterized by the turns ratio “n.”
55)
56)
The dot convention is used to establish induced voltage polarities in atransformer.
56)
57)
The input impedance to amutual inductor displays an impedance inversion behavior relative to the
load impedance.
57)
58)
The i–vof mutual inductors are characterized by two equations in four unknowns.
58)
59)
Faraday’s Law states that atime–changing electric field induces a voltage across acapacitor.
59)
60)
The transformer transforms impedance levels from one side of the transformer to the other side.
60)
61)
The transformer transforms current levels from one side of the transformer to the other side.
61)
62)
Over 90 percent of the magnetic flux links both coils in apractical transformer.
62)
63)
The changing magnetic field due to achanging current in one inductor can induce a voltage into
another, different conductor.
63)
Answer Key
Testname: C13
Answer Key
Testname: C13
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