Andrew Best
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Quiz on ELT AC quiz 1-2 , created by Andrew Best on 18/01/2018.

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ELT AC quiz 1-2

Question 1 of 53

1

The Tesla (T) and the Gauss (G) are both units for magnetic flux destiny.

Select one of the following:

  • True
  • False

Explanation

Question 2 of 53

1

The Unit for measuring magnet-motive force (mmf) is the volt.

Select one of the following:

  • True
  • False

Explanation

Question 3 of 53

1

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

Select one of the following:

  • True
  • False

Explanation

Question 4 of 53

1

A Solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.

Select one of the following:

  • True
  • False

Explanation

Question 5 of 53

1

A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).

Select one of the following:

  • True
  • False

Explanation

Question 6 of 53

1

To produce an induced voltage in a coil, the magnetic field surrounding can be changed.

Select one of the following:

  • True
  • False

Explanation

Question 7 of 53

1

The speed of a generator can be controlled with a rheostat in the field winding's.

Select one of the following:

  • True
  • False

Explanation

Question 8 of 53

1

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.

Select one of the following:

  • True
  • False

Explanation

Question 9 of 53

1

The power developed by a motor is proportional to its torque.

Select one of the following:

  • True
  • False

Explanation

Question 10 of 53

1

In a brushless motor, the magnetic field is supplied by permanent magnets.

Select one of the following:

  • True
  • False

Explanation

Question 11 of 53

1

The period of a 60 Hz sine is 16.7 ms.

Select one of the following:

  • True
  • False

Explanation

Question 12 of 53

1

The rms and average value of a sine wave are the same.

Select one of the following:

  • True
  • False

Explanation

Question 13 of 53

1

A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.

Select one of the following:

  • True
  • False

Explanation

Question 14 of 53

1

The peak value of a sine wave is the same as its amplitude.

Select one of the following:

  • True
  • False

Explanation

Question 15 of 53

1

The number of radians in 360 degrees is 2π.

Select one of the following:

  • True
  • False

Explanation

Question 16 of 53

1

In a three-phase electrical system, the phases are separated by 60°

Select one of the following:

  • True
  • False

Explanation

Question 17 of 53

1

The purpose of an exciter is to supply dc rotor current to an alternator.

Select one of the following:

  • True
  • False

Explanation

Question 18 of 53

1

In an automotive alternator, the output current is taken from the rotor through slip rings.

Select one of the following:

  • True
  • False

Explanation

Question 19 of 53

1

A maintenance issue with induction motors is brush replacement.

Select one of the following:

  • True
  • False

Explanation

Question 20 of 53

1

A synchronous motor can be used when constant speed is required.

Select one of the following:

  • True
  • False

Explanation

Question 21 of 53

1

When the south poles of two bar magnets are brought close together, there will be

Select one of the following:

  • a force of attraction

  • a force of repulsion

  • an upward force

  • no force

Explanation

Question 22 of 53

1

A magnetic field is made up of

Select one of the following:

  • positive and negative charges

  • magnetic domains

  • flux lines

  • magnetic poles

Explanation

Question 23 of 53

1

the Direction of a magnetic field is from

Select one of the following:

  • north pole to south pole

  • south pole to north pole

  • inside to outside the magnet

  • front to back

Explanation

Question 24 of 53

1

Reluctance in a magnetic circuit is analogous to

Select one of the following:

  • voltage in an electric circuit

  • current in an electric circuit

  • power in a electric circuit

  • resistance in a electric circuit

Explanation

Question 25 of 53

1

The unit of magnetic flux is

Select one of the following:

  • tesla

  • weber

  • ampere-turn

  • ampere-turns/weber

Explanation

Question 26 of 53

1

The unit of magneto-motive force is the

Select one of the following:

  • tesla

  • weber

  • ampere-turn

  • ampere-turns/ weber

Explanation

Question 27 of 53

1

The unit of flux density is the

Select one of the following:

  • tesla

  • weber

  • ampere-turn

  • electron-volt

Explanation

Question 28 of 53

1

The electromagnetic activation of a movable shaft is the basis for

Select one of the following:

  • relays

  • circuit breakers

  • magnetic switches

  • solenoids

Explanation

Question 29 of 53

1

When there is current through a wire placed in a magnetic field,

Select one of the following:

  • the wire will overheat

  • the wire will become magnetized

  • a force is exerted on the wire

  • the magnetic field will be cancelled

Explanation

Question 30 of 53

1

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

Select one of the following:

  • remain unchanged

  • decrease

  • increase

  • be excessive

Explanation

Question 31 of 53

1

if a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage induced in the conductor will

Select one of the following:

  • remain constant

  • reverse polarity

  • be reduced

  • be increased

Explanation

Question 32 of 53

1

In the crankshaft position sensor in figure 10-33, the induced voltage across the coil is caused by

Select one of the following:

  • a current in the coil

  • rotation of the steel disk

  • a tab passing through the magnetic field

  • acceleration of the steel disks rotational speed

Explanation

Question 33 of 53

1

The purpose of the commutator in a generator or motor is to

Select one of the following:

  • 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

Explanation

Question 34 of 53

1

In a motor, back emf serves to

Select one of the following:

  • increase power from the motor

  • decrease flux

  • increase the current in the field windings

  • decrease the current in the armature

Explanation

Question 35 of 53

1

The torque of a motor is proportional to the

Select one of the following:

  • amount of flux

  • armature current

  • both of the above

  • none of the above

Explanation

Question 36 of 53

1

The difference between alternating current (AC) and direct current (DC) is

Select one of the following:

  • ac changes value and dc does not

  • ac changes direction and dc does not

  • both answers A and B

  • neither answers A and B

Explanation

Question 37 of 53

1

During each cycle, a sine wave reaches a peak value

Select one of the following:

  • one time

  • two times

  • four times

  • a number of times depending on the frequency

Explanation

Question 38 of 53

1

A sine wave with a frequency of 12 kHz is changing at a faster rate than a sine wave with a frequency of

Select one of the following:

  • 20 kHz

  • 15,000 Hz

  • 10,000 Hz

  • 1.25 MHz

Explanation

Question 39 of 53

1

A sine wave with a period of 2 ms is changing at a faster rate than a sine wave with a period of

Select one of the following:

  • 1 ms

  • 0.0025 s

  • 1.5 ms

  • 1200 ms

Explanation

Question 40 of 53

1

when a sine wave has a frequency of 60 Hz, in 10 s it goes through

Select one of the following:

  • 6 cycles

  • 10 cycles

  • 1/16 cycle

  • 600 cycles

Explanation

Question 41 of 53

1

if the peak value of a sine wave is 10 V, the peak-to-peak value is

Select one of the following:

  • 20 V

  • 5V

  • 100V

  • none of these

Explanation

Question 42 of 53

1

I the peak value of a sine wave is 20V, the rms value is

Select one of the following:

  • 14.14 V

  • 6.37 V

  • 7.07 V

  • 5 V

Explanation

Question 43 of 53

1

The average value of a 10 V peak sine wave over one complete cycle is

Select one of the following:

  • 0 V

  • 6.37 V

  • 7.07 V

  • 5 V

Explanation

Question 44 of 53

1

The average half-cycle value of a sine wave with a 20 V peak is

Select one of the following:

  • 0 V

  • 6.37 V

  • 12.74 V

  • 14.14 V

Explanation

Question 45 of 53

1

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

Select one of the following:

  • 55°

  • 35°

  • 0°

  • none of these

Explanation

Question 46 of 53

1

The instantaneous value of a 15 A peak sine wave point at a 32° from its postive-going zero crossing is

Select one of the following:

  • 7.95 A

  • 7.5 A

  • 2.13 A

  • 7.95 V

Explanation

Question 47 of 53

1

A phasor represents

Select one of the following:

  • thew magnitude of a quantity

  • the magnitude and direction of a quantity

  • the phase angle

  • the length quantity

Explanation

Question 48 of 53

1

if the rms current through a 10kΩ resistor is 5 mA, the rms voltage drop across the resistors is

Select one of the following:

  • 70.7 V

  • 7.07 V

  • 5 V

  • 50V

Explanation

Question 49 of 53

1

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

Select one of the following:

  • 9.7 V

  • 9.19 V

  • 13.72 V

  • 4.53 V

Explanation

Question 50 of 53

1

An advatage of a three-phase induction motor is that it

Select one of the following:

  • maintains constant speed at any load

  • does not require starting winding's

  • has a wound rotor

  • all of the above

Explanation

Question 51 of 53

1

The difference in the synchronous speed of the stator field and the rotor speed of the motor is called

Select one of the following:

  • differential speed

  • loading

  • lag

  • slip

Explanation

Question 52 of 53

1

a 10kHz pulse waveform consists of pulses that are 10us wide. Its duty cycle is

Select one of the following:

  • 100%

  • 10%

  • 1%

  • not determinable

Explanation

Question 53 of 53

1

The duty cycle of a square wave

Select one of the following:

  • varies wit the frequency

  • varies with the pulse width

  • both answers A and B

  • is 50%

Explanation

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