11931679
Descripción
Test por Andrew Best, actualizado hace más de 1 año
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Creado por Andrew Best
hace casi 7 años
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Pregunta 1
Pregunta
The Tesla (T) and the Gauss (G) are both units for magnetic flux destiny.
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- True
- False
Pregunta 2
Pregunta
The Unit for measuring magnet-motive force (mmf) is the volt.
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- True
- False
Pregunta 3
Pregunta
Ohm's law for a magnetic circuit gives the relationship between flux destiny, magnet-motive force, and reluctance.
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- True
- False
Pregunta 4
Pregunta
A Solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.
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- True
- False
Pregunta 5
Pregunta
A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).
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- True
- False
Pregunta 6
Pregunta
To produce an induced voltage in a coil, the magnetic field surrounding can be changed.
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- True
- False
Pregunta 7
Pregunta
The speed of a generator can be controlled with a rheostat in the field winding's.
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- True
- False
Pregunta 8
Pregunta
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.
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- True
- False
Pregunta 9
Pregunta
The power developed by a motor is proportional to its torque.
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- True
- False
Pregunta 10
Pregunta
In a brushless motor, the magnetic field is supplied by permanent magnets.
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- True
- False
Pregunta 11
Pregunta
The period of a 60 Hz sine is 16.7 ms.
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- True
- False
Pregunta 12
Pregunta
The rms and average value of a sine wave are the same.
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- True
- False
Pregunta 13
Pregunta
A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.
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- True
- False
Pregunta 14
Pregunta
The peak value of a sine wave is the same as its amplitude.
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- True
- False
Pregunta 15
Pregunta
The number of radians in 360 degrees is 2π.
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- True
- False
Pregunta 16
Pregunta
In a three-phase electrical system, the phases are separated by 60°
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- True
- False
Pregunta 17
Pregunta
The purpose of an exciter is to supply dc rotor current to an alternator.
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- True
- False
Pregunta 18
Pregunta
In an automotive alternator, the output current is taken from the rotor through slip rings.
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- True
- False
Pregunta 19
Pregunta
A maintenance issue with induction motors is brush replacement.
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- True
- False
Pregunta 20
Pregunta
A synchronous motor can be used when constant speed is required.
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- True
- False
Pregunta 21
Pregunta
When the south poles of two bar magnets are brought close together, there will be
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-
a force of attraction
-
a force of repulsion
-
an upward force
-
no force
Pregunta 22
Pregunta
A magnetic field is made up of
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-
positive and negative charges
-
magnetic domains
-
flux lines
-
magnetic poles
Pregunta 23
Pregunta
the Direction of a magnetic field is from
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-
north pole to south pole
-
south pole to north pole
-
inside to outside the magnet
-
front to back
Pregunta 24
Pregunta
Reluctance in a magnetic circuit is analogous to
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-
voltage in an electric circuit
-
current in an electric circuit
-
power in a electric circuit
-
resistance in a electric circuit
Pregunta 25
Pregunta
The unit of magnetic flux is
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-
tesla
-
weber
-
ampere-turn
-
ampere-turns/weber
Pregunta 26
Pregunta
The unit of magneto-motive force is the
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-
tesla
-
weber
-
ampere-turn
-
ampere-turns/ weber
Pregunta 27
Pregunta
The unit of flux density is the
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-
tesla
-
weber
-
ampere-turn
-
electron-volt
Pregunta 28
Pregunta
The electromagnetic activation of a movable shaft is the basis for
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-
relays
-
circuit breakers
-
magnetic switches
-
solenoids
Pregunta 29
Pregunta
When there is current through a wire placed in a magnetic field,
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-
the wire will overheat
-
the wire will become magnetized
-
a force is exerted on the wire
-
the magnetic field will be cancelled
Pregunta 30
Pregunta
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
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-
remain unchanged
-
decrease
-
increase
-
be excessive
Pregunta 31
Pregunta
if a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage induced in the conductor will
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-
remain constant
-
reverse polarity
-
be reduced
-
be increased
Pregunta 32
Pregunta
In the crankshaft position sensor in figure 10-33, the induced voltage across the coil is caused by
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-
a current in the coil
-
rotation of the steel disk
-
a tab passing through the magnetic field
-
acceleration of the steel disks rotational speed
Pregunta 33
Pregunta
The purpose of the commutator in a generator or motor is to
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-
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
Pregunta 34
Pregunta
In a motor, back emf serves to
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-
increase power from the motor
-
decrease flux
-
increase the current in the field windings
-
decrease the current in the armature
Pregunta 35
Pregunta
The torque of a motor is proportional to the
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-
amount of flux
-
armature current
-
both of the above
-
none of the above
Pregunta 36
Pregunta
The difference between alternating current (AC) and direct current (DC) is
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ac changes value and dc does not
-
ac changes direction and dc does not
-
both answers A and B
-
neither answers A and B
Pregunta 37
Pregunta
During each cycle, a sine wave reaches a peak value
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one time
-
two times
-
four times
-
a number of times depending on the frequency
Pregunta 38
Pregunta
A sine wave with a frequency of 12 kHz is changing at a faster rate than a sine wave with a frequency of
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20 kHz
-
15,000 Hz
-
10,000 Hz
-
1.25 MHz
Pregunta 39
Pregunta
A sine wave with a period of 2 ms is changing at a faster rate than a sine wave with a period of
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-
1 ms
-
0.0025 s
-
1.5 ms
-
1200 ms
Pregunta 40
Pregunta
when a sine wave has a frequency of 60 Hz, in 10 s it goes through
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-
6 cycles
-
10 cycles
-
1/16 cycle
-
600 cycles
Pregunta 41
Pregunta
if the peak value of a sine wave is 10 V, the peak-to-peak value is
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-
20 V
-
5V
-
100V
-
none of these
Pregunta 42
Pregunta
I the peak value of a sine wave is 20V, the rms value is
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-
14.14 V
-
6.37 V
-
7.07 V
-
5 V
Pregunta 43
Pregunta
The average value of a 10 V peak sine wave over one complete cycle is
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-
0 V
-
6.37 V
-
7.07 V
-
5 V
Pregunta 44
Pregunta
The average half-cycle value of a sine wave with a 20 V peak is
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-
0 V
-
6.37 V
-
12.74 V
-
14.14 V
Pregunta 45
Pregunta
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
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-
55°
-
35°
-
0°
-
none of these
Pregunta 46
Pregunta
The instantaneous value of a 15 A peak sine wave point at a 32° from its postive-going zero crossing is
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-
7.95 A
-
7.5 A
-
2.13 A
-
7.95 V
Pregunta 47
Pregunta
A phasor represents
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thew magnitude of a quantity
-
the magnitude and direction of a quantity
-
the phase angle
-
the length quantity
Pregunta 48
Pregunta
if the rms current through a 10kΩ resistor is 5 mA, the rms voltage drop across the resistors is
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-
70.7 V
-
7.07 V
-
5 V
-
50V
Pregunta 49
Pregunta
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
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-
9.7 V
-
9.19 V
-
13.72 V
-
4.53 V
Pregunta 50
Pregunta
An advatage of a three-phase induction motor is that it
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-
maintains constant speed at any load
-
does not require starting winding's
-
has a wound rotor
-
all of the above
Pregunta 51
Pregunta
The difference in the synchronous speed of the stator field and the rotor speed of the motor is called
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-
differential speed
-
loading
-
lag
-
slip
Pregunta 52
Pregunta
a 10kHz pulse waveform consists of pulses that are 10us wide. Its duty cycle is
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-
100%
-
10%
-
1%
-
not determinable
Pregunta 53
Pregunta
The duty cycle of a square wave
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-
varies wit the frequency
-
varies with the pulse width
-
both answers A and B
-
is 50%
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