The inductance of an iron-core coil decreases if

The number of turns is decreased

The length of the coil decreases

The inductance of an iron-core coil decreases if%!

The number of turns is decreased

The length of the coil decreases

61 + Mcqs in Electrical Inductors in Electrical Engineering Page 1 McqOptions

1.	Inductance is the property of an inductor that produces an opposition to any change in current.
A.	True
B.	False
Answer» B. False

Discussion

2.	An induced voltage is produced as a result of a dc voltage.
A.	True
B.	False
Answer» C.

Discussion

3.	Inductors add in parallel.
A.	True
B.	False
Answer» C.

Discussion

4.	The following coils are in parallel: 75 µH, 40 µH, 25 µH, and 15 µH. The total inductance is approximately
A.	6.9 µH
B.	14 µH
C.	2.2 µH
D.	155 µH
Answer» B. 14 µH

Discussion

5.	When the current through an inductor is cut in half, the amount of energy stored in the electromagnetic field
A.	Is quartered
B.	Quadruples
C.	Doubles
D.	Does not change
Answer» B. Quadruples

Discussion

6.	When the current through an inductor decreases, the amount of energy stored in the electromagnetic field
A.	Increases
B.	Decreases
C.	Remains the same
D.	Doubles
Answer» C. Remains the same

Discussion

7.	An ohmmeter is connected across an inductor and the pointer indicates zero ohms. The inductor is
A.	Good
B.	Open
C.	Shorted
D.	Partly shorted
Answer» D. Partly shorted

Discussion

8.	Two inductors, L1 and L2, are in parallel. L1 has a value of 25 µH and L2 a value of 50 µH. The parallel combination is in series with L3, a 20 µH coil. The entire combination is across an ac source of 60 Vrms at 300 kHz. The total rms current is
A.	87 mA
B.	870 mA
C.	87 A
D.	337 mA
Answer» C. 87 A

Discussion

9.	The permeability of a core material is an indication of the ability of the material to establish a magnetic field.
A.	True
B.	False
Answer» B. False

Discussion

10.	The inductance of an iron-core coil decreases if
A.	The number of turns is decreased
B.	The iron core is removed
C.	The length of the coil decreases
D.	None of the above
Answer» B. The iron core is removed

Discussion

11.	A 240 µH inductor is equivalent to a
A.	0.240 mH inductor
B.	0.000240 mH inductor
C.	240 mH inductor
D.	240 H inductor
Answer» B. 0.000240 mH inductor

Discussion

12.	A 320 µH coil is in series with a 3.3 kΩ resistor. How long does it take for current to build up to its full value?
A.	0.48 s
B.	0.48 ms
C.	0.48 µs
D.	48 s
Answer» D. 48 s

Discussion

13.	A switch, a 220 Ω resistor, and a 60 mH inductor are in series across a 20 V battery. What is the current through the inductor two time constants after the switch is closed?
A.	91 mA
B.	78 mA
C.	57 mA
D.	400 mA
Answer» C. 57 mA

Discussion

14.	The term 'choke' is more commonly used in connection with an inductor used to block off high frequencies.
A.	True
B.	False
Answer» B. False

Discussion

15.	All coil cores are made of iron.
A.	True
B.	False
Answer» C.

Discussion

16.	XL is directly proportional to frequency and inductance.
A.	True
B.	False
Answer» B. False

Discussion

17.	Energy is stored by an inductor in an electrostatic field.
A.	True
B.	False
Answer» C.

Discussion

18.	The current through a 120 mH coil is changing at a rate of 150 mA/s. The voltage induced across the coil is
A.	1.8 mV
B.	18 mV
C.	180 mV
D.	1.25 mV
Answer» C. 180 mV

Discussion

19.	A sine wave voltage is applied across an inductor. When the frequency of the voltage is decreased, the current
A.	Is increased
B.	Is decreased
C.	Does not change
D.	Momentarily goes to zero
Answer» B. Is decreased

Discussion

20.	Inductance is indirectly proportional to the square of the number of turns, the permeability, and the cross-sectional area of the core.
A.	True
B.	False
Answer» C.

Discussion

21.	Faraday's law states that relative motion between a magnetic field and a coil induces a voltage across the coil.
A.	True
B.	False
Answer» B. False

Discussion

22.	The voltage across a coil when di/dt = 20 mA/µs and L = 8 µH is
A.	16 mV
B.	160 mV
C.	1.6 mV
D.	2.5 mV
Answer» C. 1.6 mV

Discussion

23.	An inductance of 0.43 mH is smaller than
A.	43 µH
B.	430 µH
C.	0.05 H
D.	0.00043 H
Answer» D. 0.00043 H

Discussion

24.	An inductance of 0.08 µH is larger than
A.	0.0000008 H
B.	0.000000008 H
C.	0.000008 H
D.	0.00008 mH
Answer» C. 0.000008 H

Discussion

25.	Three 15 mH inductors are in series. The total inductance is
A.	15 mH
B.	30 mH
C.	45 mH
D.	5 mH
Answer» D. 5 mH

Discussion

26.	A 2 mH, a 3.3 mH, and a 0.2 mH inductor are connected in series. The total inductance is
A.	55 mH
B.	Less than 0.2 mH
C.	Less than 5.5 mH
D.	5.5 mH
Answer» E.

Discussion

27.	Five inductors are connected in series. The lowest value is 8 µH. If the value of each inductor is twice that of the preceding one, and if the inductors are connected in order of ascending values, the total inductance is
A.	8 H
B.	32 µH
C.	64 µH
D.	248 µH
Answer» E.

Discussion

28.	An inductor, a 1 kΩ resistor, and a switch are connected in series across a 6 V battery. At the instant the switch is closed, the inductor voltage is
A.	0 V
B.	6 V
C.	12 V
D.	4 V
Answer» C. 12 V

Discussion

29.	An 18 V power supply is connected across a coil with a winding resistance of 180 Ω. Current flow in the coil is
A.	1 mA
B.	10 mA
C.	100 mA
D.	1 A
Answer» D. 1 A

Discussion

30.	An inductor and a resistor are in series with a sine wave voltage source. The frequency is set so that the inductive reactance is equal to the resistance. If the frequency is increased, then~!
A.	VR = VL
B.	VL < VR
C.	VL = VR
D.	VL > VR
Answer» E.

Discussion

31.	Inductance is the property of an inductor that produces an opposition to any change in current.~!
A.	True
B.	False
Answer» B. False

Discussion

32.	An induced voltage is produced as a result of a dc voltage.~!
A.	True
B.	False
Answer» C.

Discussion

33.	A switch, a 220 ≈í¬© resistor, and a 60 mH inductor are in series across a 20 V battery. What is the current through the inductor two time constants after the switch is closed?%!
A.	91 mA
B.	78 mA
C.	57 mA
D.	400 mA
Answer» C. 57 mA

Discussion

34.	The term 'choke' is more commonly used in connection with an inductor used to block off high frequencies.%!
A.	True
B.	False
Answer» B. False

Discussion

35.	All coil cores are made of iron.%!
A.	True
B.	False
Answer» C.

Discussion

36.	XL is directly proportional to frequency and inductance.%!
A.	True
B.	False
Answer» B. False

Discussion

37.	Energy is stored by an inductor in an electrostatic field.%!
A.	True
B.	False
Answer» C.

Discussion

38.	Two 10 H inductors are in parallel and the parallel combination is in series with a third 10 H inductor. What is the approximate total reactance when a voltage with a frequency of 7 kHz is applied across the circuit terminals?%!
A.	219 k≈í¬©
B.	66 k≈í¬©
C.	660 k≈í¬©
D.	1.3 MO
Answer» D. 1.3 MO

Discussion

39.	The current through a 120 mH coil is changing at a rate of 150 mA/s. The voltage induced across the coil is%!
A.	1.8 mV
B.	18 mV
C.	180 mV
D.	1.25 mV
Answer» C. 180 mV

Discussion

40.	A sine wave voltage is applied across an inductor. When the frequency of the voltage is decreased, the current%!
A.	Is increased
B.	Is decreased
C.	Does not change
D.	Momentarily goes to zero
Answer» B. Is decreased

Discussion

41.	Inductance is indirectly proportional to the square of the number of turns, the permeability, and the cross-sectional area of the core.%!
A.	True
B.	False
Answer» C.

Discussion

42.	Faraday's law states that relative motion between a magnetic field and a coil induces a voltage across the coil.%!
A.	True
B.	False
Answer» B. False

Discussion

43.	Inductors add in parallel.%!
A.	True
B.	False
Answer» C.

Discussion

44.	Two inductors, L1 and L2, are in parallel. L1 has a value of 25 ¬¨¬µH and L2 a value of 50 ¬¨¬µH. The parallel combination is in series with L3, a 20 ¬¨¬µH coil. The entire combination is across an ac source of 60 Vrms at 300 kHz. The total rms current is%!
A.	87 mA
B.	870 mA
C.	87 A
D.	337 mA
Answer» C. 87 A

Discussion

45.	The following coils are in parallel: 75 ¬¨¬µH, 40 ¬¨¬µH, 25 ¬¨¬µH, and 15 ¬¨¬µH. The total inductance is approximately%!
A.	6.9 ¬¨¬µH
B.	14 ¬¨¬µH
C.	2.2 ¬¨¬µH
D.	155 ¬¨¬µH
Answer» B. 14 ¬¨¬µH

Discussion

46.	The permeability of a core material is an indication of the ability of the material to establish a magnetic field.%!
A.	True
B.	False
Answer» B. False

Discussion

47.	When the current through an inductor is cut in half, the amount of energy stored in the electromagnetic field%!
A.	Is quartered
B.	Quadruples
C.	Doubles
D.	Does not change
Answer» B. Quadruples

Discussion

48.	The inductance of an iron-core coil decreases if%!
A.	The number of turns is decreased
B.	The iron core is removed
C.	The length of the coil decreases
D.	None of the above
Answer» B. The iron core is removed

Discussion

49.	When the current through an inductor decreases, the amount of energy stored in the electromagnetic field%!
A.	Increases
B.	Decreases
C.	Remains the same
D.	Doubles
Answer» C. Remains the same

Discussion

50.	A 240 ¬¨¬µH inductor is equivalent to a%!
A.	0.240 mH inductor
B.	0.000240 mH inductor
C.	240 mH inductor
D.	240 H inductor
Answer» B. 0.000240 mH inductor

Discussion

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Faraday's law states that relative motion between a magnetic field and a coil induces a voltage across the coil.%!

Inductors add in parallel.%!

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