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