Inductors MCQs : This section focuses on the "Inductors". These Multiple Choice Questions (MCQs) should be practiced to improve the Inductors skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
What is the permeability of transformer iron?
Which transformer turns ratio is needed to match two 16-ohm parallel devices to an output of 22.2 ohms?
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
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
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
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
What is the maximum source current for a transformer rated at 10 kVA, 1000/500 60 Hz?
A. 2:00 AM
B. 5:00 AM
C. 10:00 AM
D. 20 A
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
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
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
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
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
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
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
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
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
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
Fixed transformers have:
A. a center-tapped secondary
B. multiple windings
C. turns ratios that cannot be changed
D. a multiple-tapped secondary
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
The unit of flux density is:
A. magnetomotive force
B. a weber
C. a maxwell
D. a tesla
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
A practical inductor
A. has inductance
B. has winding resistance
C. has winding capacitance
D. all of the above
A winding of wire can be called
A. an inductor
B. a coil
C. a choke
D. All of the above
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.
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
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
What type of device consists of a coil with a moveable iron core?
B. reed switch
When an electromagnet reaches maximum strength, it is considered to be:
A. in field condition
B. at saturation
D. at field strength
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
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
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
The four factors determining inductance are the number of turns, coil length, coil area, and:
C. counter emf
D. coefficient of coupling
The time difference, or lag, between flux density and magnetizing force is known as:
A. eddy current
B. magnetic saturation
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
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.
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
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
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
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
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
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
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
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
When a magnet enters a coil and a voltage is induced, the process is known as:
A. an alternation
C. counter emf
D. flux linkage
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
During a current change, the ability of a conductor to produce counter emf within itself is called:
A. back emf
C. a henry
Opposition to current flow without the dissipation of energy is called:
B. inductive reactance
C. counter emf
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
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
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.
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
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
A magnetic field has:
A. polar fields
B. lines of force
C. magnetomotive force
D. lines of reluctance
What term is used to describe the action of magnetic flux from one circuit that cuts across the conductors of another circuit?
C. mutual inductance
Electromagnetic induction is the generation of:
A. electricity from magnetism
B. electricity from electricity
C. magnetism from electricity
D. magnetism from magnetism
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
With a square wave input, an RL differentiator circuit with an output across the inductor will produce what type of waveform?
B. short time-duration pulses
C. exponential-shaped pulses
D. only a phase shift
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
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
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.
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
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
What is remanence?
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
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
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
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
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
What is the name of the part inside a relay that is moved by the action of the electromagnet?
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
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
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
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.
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
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
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°)
A value of "ten to the eighth power magnetic lines of force" is for the term:
In a B-H curve, magnetizing force is equal to:
B. H = I × N
C. ampere-turns per weber
D. webers per square meter
Indication of transformer primary and secondary voltage relationships is accomplished by:
A. color-coded wires
B. dot notation
C. black, rather than gray, casings
D. winding ratios