Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
When aDC voltage source is switched on in acircuit with resistance and inductance, the voltages
and currents across the components
1)
A)
are indeterminate because the inductor is ashort.
B)
go through atransient to reach the DC steady–state values.
C)
jump to the DC steady–state values immediately.
D)
stay at zero because the inductor is ashort.
2)
An inductor opposes an instantaneous change of
2)
A)
voltage.
B)
current.
C)
resistance.
D)
None of the above
B
3)
1 H of inductance is defined as
3)
A)
1Wb of magnetic flux per ampere.
B)
1 A of current per ohm.
C)
1 V of voltage per ohm.
D)
1ampere of current per Weber.
A
4)
Lenz’s Law states that
4)
A)
the induced voltage opposes achange of current through an inductor.
B)
the induced voltage opposes achange of voltage across an inductor.
C)
the induced current opposes achange of voltage across an inductor.
D)
the induced current opposes achange of current through an inductor.
A
B
5)
Faraday’s Law relates
5)
A)
atime–changing magnetic field to an induced voltage.
B)
atime–changing electric field to an induced voltage.
C)
atime–changing electric field to an induced current.
D)
atime–changing magnetic field to an induced current.
6)
An ideal inductor
6)
A)
radiates energy.
B)
dissipates energy.
C)
stores energy.
D)
All of the above
7)
The total inductance of two inductors, 2 µH and 10 µH, in series, is
7)
A)
20 µH
B)
1.67 µH
C)
12 µH
D)
1.59 µH
8)
For two inductors in parallel, if one inductance is much larger than the other, the total inductance is
8)
A)
approximately equal to the inductance of the smaller inductor.
B)
approximately equal to the product of the inductances.
C)
approximately equal to the inductance of the larger inductor.
D)
No approximation is possible
9)
An inductor can
9)
A)
store electrical energy.
B)
return electrical energy to acircuit.
C)
Both Aand B
D)
Neither Anor B
10)
The inductance of acoil is inversely proportional to
10)
A)
the cross–sectional area.
B)
the length of the coil.
C)
the permeability.
D)
None of the above
11)
For two inductors in series, if one inductance is much larger than the other, the total inductance is
11)
A)
approximately equal to the inductance of the larger inductor.
B)
approximately equal to the product of the inductances.
C)
approximately equal to the inductance of the smaller inductor.
D)
No approximation is possible
12)
An inductor can take the form of
12)
A)
acoil.
B)
alength of wire.
C)
atoroid.
D)
All of the above
13)
The total inductance of two inductors, 2 µH and 10 µH, in parallel, is
13)
A)
1.59 µH
B)
1.67 µH
C)
12 µH
D)
20 µH
14)
There can be a voltage across an ideal inductor
14)
A)
never, because the inductor is ashort circuit.
B)
only when the circuit reaches steady–state.
C)
only at t = 0.
D)
only during the transient.
15)
The AC voltage across an inductor
15)
A)
leads the current by 90°.
B)
is in–phase with the current.
C)
is 180°out–of–phase with the current.
D)
lags the current by 90°.
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
16)
The inductance of Nidentical inductors of inductance Leach in series is ________.
16)
17)
The total inductance of two parallel inductors, 1 µH and 2 µH, that are in series with a 5 µH
inductor is ________ (give number and units).
17)
18)
The total inductance of three inductors, 1 µH, 2 µH, and 2.2 µH in series is ________ (give
number and units).
18)
19)
The energy stored in a 2 mH inductor if the current is 10 mA is ________ (give number and
units).
19)
20)
The number of turns required for acoil inductance of 30 mH with acore that has arelative
permeability of 250, across–sectional area of 17 mm2,and alength of 0.5 cm is ________
(give number and units).
20)
21)
The inductance of acoil with acore that has arelative permeability of 51, across–sectional
area of 1cm2,200turns, and alength of 1.5 cm is ________ (give number and units).
21)
22)
The total inductance of three inductors, 1 µH, 2 µH, and 2.2 µH in parallel is ________ (give
number and units).
22)
23)
The inductance of Nidentical inductors of inductance Leach in parallel is ________.
23)
24)
The total inductance of two series inductors, 5 µH and 2 µH, that are in parallel with a 1 µH
inductor is ________ (give number and units).
24)
25)
The inductance of acoil with acore that has arelative permeability of 2000, a
cross–sectional area of 0.18 in2,2000 turns, and alength of 1.5 cm is ________ (give number
and units).
25)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
26)
Atime–changing magnetic field never induces a voltage into aconductor because the magnetic
field is not moving with respect to the conductor.
26)
27)
Magnetic flux lines are solenoidal.
27)
28)
The inductances of inductors in parallel add.
28)
29)
The permeability of iron is greater than the permeability of air.
29)
30)
Magnetic flux lines form closed loops unless there is apermanent magnet involved.
30)
31)
Inductors store electrical energy in amagnetic field.
31)
32)
The inductance of acoil is directly proportional to the number of turns–squared.
32)
33)
The inductance of acoil is directly proportional to the cross–sectional area.
33)
34)
Inductors oppose an instantaneous change in current.
34)
35)
Unlike magnetic poles attract and like magnetic poles repel.
35)
36)
Moving charges create amagnetic field.
36)
37)
The inductances of inductors in series add.
37)
38)
The relative permeability is the factor by which the permeability of vacuum is greater than the
permeability of amagnetic material.
38)
39)
The inductance of acoil is directly proportional to the length.
39)
40)
The inductance of acoil is directly proportional to the permeability of the core.
40)
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
41)
Describe when Wheeler’s equation should be used.
41)
42)
Describe the difference between aresistor and an inductor from an energy viewpoint.
42)
43)
Identify and explain the phase shift between the AC voltage across and the AC current
through an inductor.
43)
44)
Describe why an inductor opposes an instantaneous change of current.
44)
45)
Describe (and/or sketch) and explain the curve of the voltage versus time when DC is
applied to acircuit with resistance and inductance.
45)
Answer Key
Testname: C6
8
Answer Key
Testname: C6
9