Inductors

Q1: Which transformer turns ratio is needed to match two 16-ohm parallel devices to an output of 22.2 ohms?

A 1.38:1

B 1.67:1

C 0.72:1

D 0.60:1

Q2: A value of "ten to the eighth power magnetic lines of force" is for the term:

A field

B flux

C coulomb

D weber

Q3: Electricity may be generated by a wire:

A carrying current

B wrapped as a coil

C that has neutral domains

D passing through a flux field

Q4: What is the phase angle of a 24 Vac parallel RL circuit when R = 45 ohms and XL = 1100 ohms?

A 0.001 degrees

B 2.300 degrees

C 87.600 degrees

D 89.900 degrees

Q5: What does Faraday's law concern?

A a magnetic field in a coil

B a magnetic field cutting a conductor

C a magnetic field hystersis

D a magnetic field in a conductor

Q6: Fixed transformers have:

A a center-tapped secondary

B multiple windings

C turns ratios that cannot be changed

D a multiple-tapped secondary

Q7: If the switch is moved to position 1 in the given circuit, how long will it take for the current to reach its maximum value?

A
72.5 mu.gifs

B
532 mu.gifs

C
610 mu.gifs

D
833 mu.gifs

Q8: What will happen when an inductor's magnetic field collapses?

A Current will double.

B Voltage will be induced.

C A new field will expand.

D Counter emf will be high.

Q9: What is hysteresis?

A lead between cause and effect

B lag between cause and effect

C lead between voltage and current

D lag between voltage and current

Q10: How long until the current is at a maximum?

mcq8_1032_1.gif

A
0 mu.jpgs

B
5 mu.jpgs

C
15 mu.jpgs

D
25 mu.jpgs

Q11: What is the total inductance of a 5 H and a 100 mH coil connected in parallel?

A
4.76 mH

B
33.3 mH

C
98.0 mH

D
150.0 mH

Q12: If the primary of a 4:1 turns transformer dissipates 5 W, what is the secondary power?

A
5.0 W

B
1.25 pW

C
9.5 W

D
20.0 mW

Q13: During a current change, the ability of a conductor to produce counter emf within itself is called:

A back emf

B self-induction

C a henry

D impedance

Q14: Find VR and VL.

mcq8_1034_1.gif

A
VR = 41.6 V, VL = 78.4 V

B
VR = 48 V, VL = 110 V

C
VR = 56 V, VL = 106 V

D
VR = 60 V, VL = 60 V

Q15: What is the permeability of transformer iron?

A 50

B 450

C 1500

D 5500

Q16: Which two values are plotted on a B-H curve graph?

A reluctance and flux density

B permeability and reluctance

C magnetizing force and permeability

D flux density and magnetizing force

Q17: A turns ratio of 5 for a transformer implies:

A more primary turns than secondary turns

B more secondary current than primary current

C larger source impedance than load impedance

D more secondary turns than primary turns

Q18: Which coil would be used as a step-up transformer primary if coil number 1 has 100 more turns than coil number 2?

A The coil windings must be the same.

B coil 1

C The coil ratio is too small.

D coil 2

Q19: The unit of flux density is:

A magnetomotive force

B a weber

C a maxwell

D a tesla

Q20: When the transformer secondary is not loaded:

A secondary voltage increases

B no secondary current flows

C no secondary voltage is present

D secondary current increases

Q21: What is remanence?

A reactance

B reluctance

C retentitivity

D resistance

Q22: When current in an inductor starts to change, it cannot react instantly due to:

A fixed coil resistance

B eddy current generation

C applied emf of the circuit

D the counter emf of the coil

Q23: A winding of wire can be called

A an inductor

B a coil

C a choke

D All of the above

Q24: When an electromagnet reaches maximum strength, it is considered to be:

A in field condition

B at saturation

C inhibited

D at field strength

Q25: A loaded transformer will achieve mutual induction when:

A secondary current increase causes a primary current decrease

B primary current is increased by an increase in secondary current

C primary current is decreased by an increase in secondary current

D secondary current decrease causes a primary current increase

Q26: A transformer will have:

A primary and secondary windings

B primary and secondary current

C primary wattage producing secondary current

D different frequencies for the primary and secondary

Q27: What is the permeability of machine steel?

A
1.1 x 10−4

B
5.65 x 10−4

C
6.9 x 10−3

D
8.8 x 10−3

Q28: What is the total inductance, assuming no mutual inductance?

mcq8_1030_1.gif

A
12 mH

B
6 mH

C
0.73 mH

D
0 mH

Q29: The electrical energy consumed by a coil is stored in the form of:

A an electrical field

B a force field

C an electrostatic field

D a magnetic field

Q30: A henry value divided by a circuit resistive value provides the:

A counter emf value

B induced voltage amplitude

C rise or decay time constant

D quality factor of the coil

Q31: In a transformer, what will happen to the primary current if the secondary magnetic field increases?

A
Ip will increase.

B
Ip will be canceled.

C
Ip will remain the same.

D
Ip will decrease.

Q32: A change of one ampere per second in an inductor that induces a voltage of one volt is considered as which unit value?

A a lenz

B an ohm

C a farad

D a henry

Q33: What is electromagnetism?

A the magnetic field generated around a conductor when a current passes through it

B the magnetic field generated in a conductor by an external voltage

C the voltage caused by a magnetic field in a conductor

D the current generated by an external magnetic field

Q34: What is the inductive reactance?

mcq8_1033_1.gif

A
5.2 omega.gif

B
7.5 omega.gif

C
1.3 komega.gif

D
7.5 komega.gif

Q35: What is the current rise after 2 time constants if Vs = 12 V dc, R = 60 omega.gif, and the inductor is rated at 24 mH?

A
79.9 mA

B
126.4 mA

C
173.0 mA

D
198.6 mA

Q36: In the given circuit, what will the voltage be across R3 25 mu.gifs after the switch is moved to position 2?

A
2.88 V

B
5.9 V

C
8.34 V

D
14 V

Q37: Inductance is:

A directly proportional to the length of the coil

B directly proportional to the number of turns on the coil

C inversely proportional to the cross-sectional area of the coil

D inversely proportional to the permeability

Q38: Which of the following represents a true equivalent of an inductor?

A An inductance in series with a resistance and a capacitance

B A capacitance in parallel with the series combination of a resistance and an inductance

C An inductance in parallel with the series combination of a resistance and a capacitance

D The only quality a real inductor has is inductance.

Q39: If you wanted to decrease the inductance of a coil, you might increase the:

A number of turns

B permeability of the core

C spacing between turns

D area of the coil

Q40: What term is used to describe the action of magnetic flux from one circuit that cuts across the conductors of another circuit?

A self-inductance

B rectification

C mutual inductance

D magnetism

Q41: On a schematic, dashed lines between two vertical coils usually mean the transformer has:

A an air core

B an iron core

C a nonmetallic core

D a ferrite core

Q42: The four factors determining inductance are the number of turns, coil length, coil area, and:

A permeability

B reluctance

C counter emf

D coefficient of coupling

Q43: What is the number of turns required in the secondary winding for a transformer when 120 volts is applied to a 2400-turn primary to produce 7.5 Vac at the secondary?

A 75 turns

B 150 turns

C 900 turns

D 1920 turns

Q44: What is the maximum source current for a transformer rated at 10 kVA, 1000/500 60 Hz?

A
2 A

B
5 A

C
10 A

D
20 A

Q45: The output phase for a transformer is:

A in phase with the input

B out of phase with the input

C dependent on the direction of the primary and secondary windings

D dependent on the frequency of the primary source

Q46: When used as a filter, an inductor is

A placed in series with the load and aids any current changes

B placed in parallel with the load and aids any current changes

C placed in parallel with the load and opposes any current changes

D placed in series with the load and opposes any current changes

Q47: What is the impedance of a 1 kHz series RL circuit when R and XL are both 1000 ohms?

A
500 ohms

B
1000 ohms

C
1414 ohms

D
2000 ohms

Q48: In a B-H curve, magnetizing force is equal to:

A
mcq8_1001_1.gif

B
H = I × N

C
ampere-turns per weber

D
webers per square meter

Q49: A transformer is used:

A to couple electric energy from one dc circuit to another

B to couple electric energy from an ac circuit to a dc circuit

C to couple electric energy from a dc circuit to an ac circuit

D to couple electric energy from one ac circuit to another

Q50: When a coil collapses the induced circuit current will:

A be in the same direction

B go to zero

C aid counter emf buildup

D be in the opposite direction

Q51: Find IR and IL.

mcq8_1035_1.gif

A
IR = 50 mA, IL = 109 mA

B
IR = 150 mA, IL = 9 mA

C
IR = 50 mA, IL = 151 mA

D
IR = 150 mA, IL = 53 mA

Q52: Counter emf or induced voltage is:

A inversely proportional to the change in current

B directly proportional to the change in time

C directly proportional to the inductance in henrys

D inversely proportional to the inductance in henrys

Q53: When a load is not connected to the secondary of a transformer:

A primary current is zero

B primary current is inversely proportional to primary impedance

C secondary voltage is zero

D secondary voltage is proportional to primary impedance

Q54: A magnetic circuit breaker will open to protect equipment only when:

A voltage is exceeded

B an open is in the equipment

C the equipment is operating properly

D current is exceeded

Q55: What is electromagnetism?

A the magnetic field generated around a conductor when a current passes through it

B the magnetic field generated in a conductor by an external voltage

C the voltage caused by a magnetic field in a conductor

D the current generated by an external magnetic field

Q56: Electromagnetism is the:

A magnetic field caused by a permanent magnet

B action between a permanent and an artificial magnet

C magnetic field action with a current-carrying wire

D current in the coil

Q57: A magnetic field has:

A polar fields

B lines of force

C magnetomotive force

D lines of reluctance

Q58: What are the properties that determine the inductance of a coil?

A Length of wire, number of turns, type of core material, length of core

B Number of turns, type of wire, length of core, and cross-sectional area of core

C Type of core material, number of turns, cross-sectional area of core, and length of core

D Type of core material, type of wire, number of turns, and cross-sectional area of core

Q59: Opposition to current flow without the dissipation of energy is called:

A resistance

B inductive reactance

C counter emf

D impedance

Q60: What is magnetic flux?

A the number of lines of force in webers

B the number of lines of force in maxwells

C the number of lines of force in teslas

D the number of lines of force in flux density

Q61: When a transformer secondary lead has been connected to a middle loop that is not an end connector, it is called a:

A multiple-tapped secondary

B center-tapped secondary

C multiple winding secondary

D single winding secondary

Q62: What happens when moving expanding lines of force encounter a conductor?

A Current increases.

B Voltage is induced.

C Resistance is reduced.

D Power is increased.

Q63: As current travels within a conductor:

A the magnetic field aids the current

B a magnetic field is developed around it

C the wire tries to point north

D an electrostatic field opposes the current

Q64: With 100 Vac applied to the primary of a transformer so that it draws 500 mA, what will be the 300 Vac secondary current?

A
1500 mA

B
200 mA

C
167 mA

D
150 mA

Q65: The time difference, or lag, between flux density and magnetizing force is known as:

A eddy current

B magnetic saturation

C hysteresis

D coercivity

Q66: Faraday's law states that the:

A direction of the induced voltage produces an opposition

B direction of an induced current produces an aiding effect

C emf depends on the rate of cutting flux

D emf is related to the direction of the current

Q67: When used as a filter, an inductor is

A placed in series with the load and aids any current changes

B placed in parallel with the load and aids any current changes

C placed in parallel with the load and opposes any current changes

D placed in series with the load and opposes any current changes

Q68: A 24 V peak source is connected across a 900 mu.gifH inductor. If the frequency of the source is 22 kHz, what is the reactive power?

A 2.3 VAR

B 4.6 VAR

C 9.3 VAR

D 0 VAR

Q69: Reactance in an inductive circuit will:

A increase with frequency

B decrease with frequency

C be independent from frequency

D
depend on the value of XC

Q70: A practical inductor

A has inductance

B has winding resistance

C has winding capacitance

D all of the above

Q71: Which of the following is NOT one of the three major types of fixed inductor?

A air core

B ferrite core

C magnesium core

D iron core

Q72: When a transformer secondary lead has been connected to a middle loop that is not an end connector, it is called a:

A multiple-tapped secondary

B center-tapped secondary

C multiple winding secondary

D single winding secondary

Q73: What is the phase angle between the source voltage and current, when a 100 mH inductor with a reactance of 6 komega.gif, and a 1 komega.gif resistor are in series with a source?

A
0.1 degrees

B
9.0 degrees

C
61.0 degrees

D
81.0 degrees

Q74: A series RL filter circuit with an output across the inductor will result in what type of filtering?

A passing of the higher frequencies

B passing of the lower frequencies

C blocking of the higher frequencies

D blocking of a certain range of frequencies

Q75: An inductor is in series with a voltage source, an open switch, and a resistor. The instant the switch is closed, the inductor acts like

A a short

B an open

C a resistor

D a voltage source

Q76: What is the total inductance assuming no mutual inductance?

mcq8_1031_1.gif

A
0 mH

B
0.69 mH

C
12 mH

D
24 mH

Q77: When a magnet enters a coil and a voltage is induced, the process is known as:

A an alternation

B self-inductance

C counter emf

D flux linkage

Q78: As a generator armature passes the 270 degree point, the induced voltage is:

A at maximum negative

B between maximum negative and zero

C at maximum positive

D between zero and maximum positive

Q79: What is the total inductance in the given circuit?

A
160 mH

B
300 mH

C
900 mH

D
1700 mH

Q80: Electromagnetic induction is the generation of:

A electricity from magnetism

B electricity from electricity

C magnetism from electricity

D magnetism from magnetism

Q81: The polarity of induced voltage while a field is collapsing is:

A independent of the force creating it

B opposite to the force creating it

C identical to the force creating the field

D present only if the force is stationary

Q82: What is the inductive reactance if the Q of a coil is 60, and the winding resistance is 5 omega.gif?

A
0.083 omega.gif

B
12 omega.gif

C
30 omega.gif

D
300 omega.gif

Q83: The time required for one weber of flux to cut a conductor and produce one volt is:

A one revolution

B one second

C one millisecond

D four revolutions

Q84: The unit of flux density is:

A magnetomotive force

B a weber

C a maxwell

D a tesla

Q85: What type of device consists of a coil with a moveable iron core?

A solenoid

B reed switch

C relay

D armature

Q86: A voltage is induced in a transformer secondary winding by the action of the:

A secondary magnetic field

B primary turns ratio

C primary magnetic field

D secondary counter emf

Q87: Current will cause a magnetic field in a conductor as follows:

A An ac current causes a fixed polarity magnetic field.

B A dc current causes a fixed polarity magnetic field.

C A dc current causes an alternating magnetic field.

D An ac current causes a fixed polarity magnetic field and a dc current causes an alternating magnetic field.

Q88: What is the approximate time for a complete decay of 400 mA of inductor current, when R = 10 ohms and L = 20 H?

A 10 seconds

B 8 seconds

C 4 seconds

D 2 seconds

Q89: With a square wave input, an RL differentiator circuit with an output across the inductor will produce what type of waveform?

A dc

B short time-duration pulses

C exponential-shaped pulses

D only a phase shift

Q90: In a purely inductive circuit,

A current leads voltage by 90°

B voltage lags current by 90°

C voltage leads current by 90°

D voltage and current are in phase (0°)

Q91: A utility pole transformer used to supply a residential customer with two phases uses:

A two phases on the primary

B a center tap on the secondary

C a separate ground for each phase

D a small coefficient of coupling

Q92: If 360 Vac is the output of a 300-turn secondary winding, what is the input voltage when the primary winding has 150 turns?

A
2.4 Vac

B
150 Vac

C
180 Vac

D
720 Vac

Q93: What is the name of the part inside a relay that is moved by the action of the electromagnet?

A armature

B conductor

C contacts

D solenoid

Q94: You could decrease the time constant of an RL circuit by

A adding a resistor in parallel with the circuit resistance

B adding an inductor in series with the circuit inductance

C decreasing the amplitude of the input voltage

D exchanging the position of the resistor and inductor in the circuit

Q95: When a rate of one ampere per second causes an induced voltage of one volt, the unit of measure is

A a lenz

B an ohm

C a farad

D a henry

Q96: A loaded transformer will achieve mutual induction when:

A secondary current increase causes a primary current decrease

B primary current is increased by an increase in secondary current

C primary current is decreased by an increase in secondary current

D secondary current decrease causes a primary current increase


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