Deck 11: Inductors

Question 1

The energy stored in an inductor's electromagnetic field is produced by the inductor's current.

Answer 1

True

Question 2

An inductor is placed in series with the load for power supply filtering.

Answer 2

True

Question 3

The total inductance of two parallel inductors equals the sum of their inductance values.

Answer 3

False

Question 4

What is the total inductance if a 50 mH inductor is connected in series with a 15 mH inductor?

A)50 mH
B)65 mH
C)11.5 mH
D)15 mH

Question 5

The voltage leads the current in an inductive circuit.

Question 6

The voltage and current are in phase in an inductive circuit.

Question 7

What is the maximum current in a 12 mH inductor if it is connected in series with a 10 kΩ resistor and a 15 VDC source?

A)2.2 mA
B)1.2 mA
C)6.32 mA
D)1.5 mA

Question 8

True power for an inductor is measured in VAR rather than watts.

Question 9

When a DC voltage is first applied to an inductor, the initial circuit current is zero.

Question 10

Inductive reactance decreases as frequency increases.

Question 11

If an inductor has an ac current flowing through it, the magnetic field is .

A)collapsed
B)steady
C)moving from south to north
D)constantly changing

Question 12

If an inductor is placed in an ac circuit, the ac voltage across the inductor leads the ac current through it.

Question 13

An inductor passes direct current and opposes alternating current.

Question 14

Do iron -core inductors or air -core inductors generally have the larger inductance?

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.

Question 15

The quality factor for an inductor becomes more apparent at higher frequencies.

Question 16

Inductors in series or parallel combine just like resistors in series or parallel.

Question 17

Inductors can radiate electromagnetic energy to other components in a system.

Question 18

If a 50 mH inductor operates at 22 kHz, XL equals .

A)1100 Ω
B)500 Ω
C)113 Ω
D)6912 Ω

Question 19

The energy stored in an inductor's electromagnetic field is produced by the resistance of the inductor's winding.

Question 20

An iron -core inductor is used in low frequency applications.

Question 21

If two inductors are connected in a series AC circuit, which inductor drops more voltage?

A)It depends upon the frequency.
B)It depends upon the source voltage.
C)the larger inductance
D)the smaller inductance

Question 22

An 0.05 µH inductance is larger than a _.

A)0.000005 H inductance
B)0.00005 H inductance
C)0.0000005 H inductance
D)0.000000008 H inductance

Question 23

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?

A)4 V
B)0 V
C)6 V
D)12 V

Question 24

What is the total inductance of a 40 mH inductor and a 24 mH inductor connected in parallel?

A)32 mH
B)150 mH
C)64 mH
D)15 mH

Question 25

Connecting a inductance. inductor in
With a 100 m H inductor produces a 65 m H

A)35 mH, series
B)186 mH, series
C)35 mH, parallel
D)186 mH, parallel

Question 26

What is the inductive reactance of a 150 mH inductor operating at 10 kHz?

A)6280 Ω
B)9420 Ω
C)8450 Ω
D)1500 Ω

Question 27

What is the total inductance of four 10 mH inductors connected in series?

A)2.5 mH
B)40 mH
C)40,000 µH
D)250 mH

Question 28

What is one time constant for a 10 mH inductor connected in series with a 47 kΩ resistor?

A)213 µS
B)470 S
C)0.213 µS
D)470 mS

Question 29

A 0.33 mH inductance is smaller than a _.

A)33 pH inductance
B)0.05 mH inductance
C)330 pH inductance
D)0.0005 H inductance

Question 30

What is the inductive reactance of a 0.2 mH inductor operating at 1 kHz?

A)1.26 Ω
B)1.26 kΩ
C)126 kΩ
D)126 Ω

Question 31

What is the total inductance of a 14 mH, 22 mH and 45 mH inductor connected in series?

A)81 µH
B)81 mH
C)7.2 mH
D)20 mH

Question 32

How many time constants will it take to completely collapse an inductor's magnetic field?

A)1
B)4
C)3
D)5

Question 33

If an inductor carries 100 mADC of current when connected across a 30 VDC source, then what is its resistance?

A)0 Ω
B)300 Ω
C)30 Ω
D)60 Ω

Question 34

If two 2.5 mH inductors are connected in series with a 4.7 kΩ resistor and the source voltage is 100 VDC, what is the circuit's maximum current?

A)1.1 mA
B)21.3 mA
C)63.2 mA
D)7.9 mA

Question 35

In an inductive circuit, the lags the .

A)voltage, reactance
B)current, resistance
C)voltage, resistance
D)current, voltage

Question 36

What is the inductive reactance of an inductor that drops 12 VRMS and carries 50 mARMS?

A)240 Ω
B)60 Ω
C)600 Ω
D)6 Ω

Question 37

If a 1 mH, 3.3 mH, and 0.1 mH inductor are connected in parallel, LT equals .

A)less than 0.1 mH
B)5.3 mH
C)4.4 mH
D)greater than 3.3 mH

Question 38

What is the inductance of a 20 mH inductor connected in parallel with a 50 mH inductor?

A)50 mH
B)70 mH
C)20 mH
D)14.3 mH

Question 39

If a 27 m H inductor has a reactance of 5.5 kΩ, the frequency equals .

A)3.24 kHz
B)324 Hz
C)932 Hz
D)32.4 kHz

Question 40

What is the time constant for a 50 mH inductor and 5 kΩ resistor connected in series?

A)10 µs
B)250 s
C)100 s
D)10 ms

Question 41

If a 50 mH inductor is in series with a 50 kΩ resistor across a 50 VDC source, what is the maximum current that will flow in the circuit?

A)10 mA
B)1 µA
C)1 mA
D)100 µA

Question 42

Reactive power (Pr)in an inductor is defined as the rate at which an inductor stores or returns energy and is measured in:

A)current per time constant.
B)volt -ampere reactive.
C)watts reactive.
D)volts per time constant.

Question 43

Connecting a inductor in
With a 70 mH inductor produces a 100 mH inductance.

A)233 mH, series
B)233 mH, parallel
C)30 mH, series
D)30 mH, parallel

Question 44

How many time constants will it take to completely build a magnetic field around an inductor?

A)1
B)2
C)3
D)4
E)5

Question 45

In a switch -mode power supply the role of the inductor is

A)surge protection
B)to produce a constant load current
C)to function as a low -pass filter
D)to function as a high -pass filter

Question 46

What is the total inductance of a 25 mH inductor connected in parallel with a 100 mH inductor?

A)less than 20 mH
B)more than 125 mH
C)20 mH
D)125 mH

Question 47

If a 25 mH inductor drops 50 V while operating at 400 Hz, what is XL?

A)6.28 kΩ
B)62.8 kΩ
C)628 Ω
D)62.8 Ω

Question 48

Which type of inductor core material is likely to produce the least inductance?

A)air
B)iron
C)ferrite

Question 49

When inductors are connected in series, their total inductance acts like:

A)resistance connected in series -parallel.
B)resistance connected in parallel.
C)resistance connected in series.
D)all of these.

Question 50

When inductors are connected in parallel, their total inductance acts like:

A)resistance connected in parallel.
B)resistance connected in series -parallel.
C)resistance connected in series.
D)all of these.

Question 51

What is the total inductance in Figure 11 -1?

A)95 mH
B)15.8 mH
C)225 mH
D)12.7 mH

Question 52

Inductors .

A)pass direct current
B)have high reactance to direct current
C)block direct current
D)have a high resistance to direct current

Question 53

The time constant for an inductor for each time period:

A)is a constant value.
B)corresponds to a 37% of the decrease in value.
C)corresponds to a 63% of the increase in value.
D)all of these.

Question 54

How much current flows in the circuit in Figure 11 -1 if connected to a 12 VPP, 2 kHz source?

A)60.5 mAp -p
B)4.77 mAp -p
C)126 mAp -p
D)10.1 mAp -p

Question 55

If a 15 µH inductor has a 2.2 KΩ reactance, the frequency equals .

A)23.3 kHz
B)4.28 MHz
C)4.28 kHz
D)23.3 MHz

Question 56

What is the reactance of a 100 µH inductor operating at 100 kHz?

A)62.8 kΩ
B)6.28 Ω
C)62.8 Ω
D)infinite Ω

Question 57

In an inductive AC circuit, the phase relationship between the voltage and the current is such that the:

A)voltage is lagging the current.
B)voltage is 360 degrees out of phase with voltage.
C)current is 180 degrees out of phase with voltage.
D)current is lagging the voltage.

Question 58

The time constant of an inductor is:

A)the time required for voltage or current to increase to 63% or to decrease to 37%.
B)inversely proportional to the resistance in the circuit.
C)directly proportional to the inductance in the circuit.
D)all of these.

Question 59

If an inductor carries 150 mADC of current when connected across a 65 VDC source, what is its resistance?

A)30 Ω
B)26.7 Ω
C)433 Ω
D)65 Ω

Question 60

What is the reactance of an inductor that carries 1.25 mAP and drops 25 VP at 100 Hz?

A)20 kΩ
B)3.13 kΩ
C)15.7 kΩ
D)31.3 Ω

Question 61

The ripple voltage as measured at the output of a power supply has increased. Which of the following could be the problem?

A)load resistance has dropped
B)partial shorting of the windings of the filtering coil
C)resistance of the coil has decreased
D)either A or B

Question 62

It has been determined that the source of audible noise for a radio is due to the power supply voltage. How can an inductor be configured to eliminate this noise?

A)An inductor will not affect the noise.
B)Connect the inductor in series with the radio power wire.
C)Connect the inductor in parallel with the radio.
D)both B and C

Question 63

Determination of an inductor's value can be had by what method(s)?

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

Question 64

The most commonplace use for inductors in electronics:

A)blocks DC voltages.
B)blocks AC voltages.
C)passes DC voltages.
D)passes AC voltages.

Question 65

Stray capacitance for a coil becomes a problem:

A)with high frequencies.
B)with low frequencies.
C)with ac circuits.
D)at resonant frequencies.

Question 66

An inductor can be simulated using resistors, capacitors, and operational amplifiers. Ths circuit is called a _ _.

A)oscillator
B)gyrator
C)modulator
D)inducer