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ELT AC quiz 1-2

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Quiz on ELT AC quiz 1-2 , created by Andrew Best on 18/01/2018.
Andrew Best
Quiz by Andrew Best, updated more than 1 year ago
Andrew Best
Created by Andrew Best almost 7 years ago
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Resource summary

Question 1

Question
The Tesla (T) and the Gauss (G) are both units for magnetic flux destiny.
Answer
  • True
  • False

Question 2

Question
The Unit for measuring magnet-motive force (mmf) is the volt.
Answer
  • True
  • False

Question 3

Question
Ohm's law for a magnetic circuit gives the relationship between flux destiny, magnet-motive force, and reluctance.
Answer
  • True
  • False

Question 4

Question
A Solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.
Answer
  • True
  • False

Question 5

Question
A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).
Answer
  • True
  • False

Question 6

Question
To produce an induced voltage in a coil, the magnetic field surrounding can be changed.
Answer
  • True
  • False

Question 7

Question
The speed of a generator can be controlled with a rheostat in the field winding's.
Answer
  • True
  • False

Question 8

Question
A self-excited dc generator will normally have enough residual magnetism in the the field magnets to start the generator producing voltage at the output when it is first turned on.
Answer
  • True
  • False

Question 9

Question
The power developed by a motor is proportional to its torque.
Answer
  • True
  • False

Question 10

Question
In a brushless motor, the magnetic field is supplied by permanent magnets.
Answer
  • True
  • False

Question 11

Question
The period of a 60 Hz sine is 16.7 ms.
Answer
  • True
  • False

Question 12

Question
The rms and average value of a sine wave are the same.
Answer
  • True
  • False

Question 13

Question
A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.
Answer
  • True
  • False

Question 14

Question
The peak value of a sine wave is the same as its amplitude.
Answer
  • True
  • False

Question 15

Question
The number of radians in 360 degrees is 2π.
Answer
  • True
  • False

Question 16

Question
In a three-phase electrical system, the phases are separated by 60°
Answer
  • True
  • False

Question 17

Question
The purpose of an exciter is to supply dc rotor current to an alternator.
Answer
  • True
  • False

Question 18

Question
In an automotive alternator, the output current is taken from the rotor through slip rings.
Answer
  • True
  • False

Question 19

Question
A maintenance issue with induction motors is brush replacement.
Answer
  • True
  • False

Question 20

Question
A synchronous motor can be used when constant speed is required.
Answer
  • True
  • False

Question 21

Question
When the south poles of two bar magnets are brought close together, there will be
Answer
  • a force of attraction
  • a force of repulsion
  • an upward force
  • no force

Question 22

Question
A magnetic field is made up of
Answer
  • positive and negative charges
  • magnetic domains
  • flux lines
  • magnetic poles

Question 23

Question
the Direction of a magnetic field is from
Answer
  • north pole to south pole
  • south pole to north pole
  • inside to outside the magnet
  • front to back

Question 24

Question
Reluctance in a magnetic circuit is analogous to
Answer
  • voltage in an electric circuit
  • current in an electric circuit
  • power in a electric circuit
  • resistance in a electric circuit

Question 25

Question
The unit of magnetic flux is
Answer
  • tesla
  • weber
  • ampere-turn
  • ampere-turns/weber

Question 26

Question
The unit of magneto-motive force is the
Answer
  • tesla
  • weber
  • ampere-turn
  • ampere-turns/ weber

Question 27

Question
The unit of flux density is the
Answer
  • tesla
  • weber
  • ampere-turn
  • electron-volt

Question 28

Question
The electromagnetic activation of a movable shaft is the basis for
Answer
  • relays
  • circuit breakers
  • magnetic switches
  • solenoids

Question 29

Question
When there is current through a wire placed in a magnetic field,
Answer
  • the wire will overheat
  • the wire will become magnetized
  • a force is exerted on the wire
  • the magnetic field will be cancelled

Question 30

Question
A coil of wire is placed on a changing magnetic field. if the number of turns ion the coil is increased, the voltage induced across the coil will
Answer
  • remain unchanged
  • decrease
  • increase
  • be excessive

Question 31

Question
if a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage induced in the conductor will
Answer
  • remain constant
  • reverse polarity
  • be reduced
  • be increased

Question 32

Question
In the crankshaft position sensor in figure 10-33, the induced voltage across the coil is caused by
Answer
  • a current in the coil
  • rotation of the steel disk
  • a tab passing through the magnetic field
  • acceleration of the steel disks rotational speed

Question 33

Question
The purpose of the commutator in a generator or motor is to
Answer
  • change the direction of the current to the rotor as it spins
  • change the direction of the current to the stator winding's
  • support the motor or generator shaft
  • provide the magnetic field for the motor or generator

Question 34

Question
In a motor, back emf serves to
Answer
  • increase power from the motor
  • decrease flux
  • increase the current in the field windings
  • decrease the current in the armature

Question 35

Question
The torque of a motor is proportional to the
Answer
  • amount of flux
  • armature current
  • both of the above
  • none of the above

Question 36

Question
The difference between alternating current (AC) and direct current (DC) is
Answer
  • ac changes value and dc does not
  • ac changes direction and dc does not
  • both answers A and B
  • neither answers A and B

Question 37

Question
During each cycle, a sine wave reaches a peak value
Answer
  • one time
  • two times
  • four times
  • a number of times depending on the frequency

Question 38

Question
A sine wave with a frequency of 12 kHz is changing at a faster rate than a sine wave with a frequency of
Answer
  • 20 kHz
  • 15,000 Hz
  • 10,000 Hz
  • 1.25 MHz

Question 39

Question
A sine wave with a period of 2 ms is changing at a faster rate than a sine wave with a period of
Answer
  • 1 ms
  • 0.0025 s
  • 1.5 ms
  • 1200 ms

Question 40

Question
when a sine wave has a frequency of 60 Hz, in 10 s it goes through
Answer
  • 6 cycles
  • 10 cycles
  • 1/16 cycle
  • 600 cycles

Question 41

Question
if the peak value of a sine wave is 10 V, the peak-to-peak value is
Answer
  • 20 V
  • 5V
  • 100V
  • none of these

Question 42

Question
I the peak value of a sine wave is 20V, the rms value is
Answer
  • 14.14 V
  • 6.37 V
  • 7.07 V
  • 5 V

Question 43

Question
The average value of a 10 V peak sine wave over one complete cycle is
Answer
  • 0 V
  • 6.37 V
  • 7.07 V
  • 5 V

Question 44

Question
The average half-cycle value of a sine wave with a 20 V peak is
Answer
  • 0 V
  • 6.37 V
  • 12.74 V
  • 14.14 V

Question 45

Question
One sine wave has positive-going zero crossing at 10° and another sine wave has a postive going zero crossing at 45°. The phase angle between the two wave-forms is
Answer
  • 55°
  • 35°
  • 0°
  • none of these

Question 46

Question
The instantaneous value of a 15 A peak sine wave point at a 32° from its postive-going zero crossing is
Answer
  • 7.95 A
  • 7.5 A
  • 2.13 A
  • 7.95 V

Question 47

Question
A phasor represents
Answer
  • thew magnitude of a quantity
  • the magnitude and direction of a quantity
  • the phase angle
  • the length quantity

Question 48

Question
if the rms current through a 10kΩ resistor is 5 mA, the rms voltage drop across the resistors is
Answer
  • 70.7 V
  • 7.07 V
  • 5 V
  • 50V

Question 49

Question
Two series resistors are connected to an AC source, If there are 6.5 V rms across one resistor and 3.2 V rms across the other, the peak source voltage is
Answer
  • 9.7 V
  • 9.19 V
  • 13.72 V
  • 4.53 V

Question 50

Question
An advatage of a three-phase induction motor is that it
Answer
  • maintains constant speed at any load
  • does not require starting winding's
  • has a wound rotor
  • all of the above

Question 51

Question
The difference in the synchronous speed of the stator field and the rotor speed of the motor is called
Answer
  • differential speed
  • loading
  • lag
  • slip

Question 52

Question
a 10kHz pulse waveform consists of pulses that are 10us wide. Its duty cycle is
Answer
  • 100%
  • 10%
  • 1%
  • not determinable

Question 53

Question
The duty cycle of a square wave
Answer
  • varies wit the frequency
  • varies with the pulse width
  • both answers A and B
  • is 50%
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