Test
ELT AC quiz 1-2
Preguntas del test (53)
1The Tesla (T) and the Gauss (G) are both units for magnetic flux destiny.
- AVerdadero
- BFalso
2The Unit for measuring magnet-motive force (mmf) is the volt.
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3Ohm's law for a magnetic circuit gives the relationship between flux destiny, magnet-motive force, and reluctance.
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4A Solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.
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5A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).
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6To produce an induced voltage in a coil, the magnetic field surrounding can be changed.
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7The speed of a generator can be controlled with a rheostat in the field winding's.
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8A 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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9The power developed by a motor is proportional to its torque.
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10In a brushless motor, the magnetic field is supplied by permanent magnets.
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11The period of a 60 Hz sine is 16.7 ms.
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12The rms and average value of a sine wave are the same.
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13A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.
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14The peak value of a sine wave is the same as its amplitude.
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15The number of radians in 360 degrees is 2π.
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16In a three-phase electrical system, the phases are separated by 60°
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17The purpose of an exciter is to supply dc rotor current to an alternator.
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18In an automotive alternator, the output current is taken from the rotor through slip rings.
- AVerdadero
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19A maintenance issue with induction motors is brush replacement.
- AVerdadero
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20A synchronous motor can be used when constant speed is required.
- AVerdadero
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21When the south poles of two bar magnets are brought close together, there will be
- Aa force of attraction
- Ba force of repulsion
- Can upward force
- Dno force
22A magnetic field is made up of
- Apositive and negative charges
- Bmagnetic domains
- Cflux lines
- Dmagnetic poles
23the Direction of a magnetic field is from
- Anorth pole to south pole
- Bsouth pole to north pole
- Cinside to outside the magnet
- Dfront to back
24Reluctance in a magnetic circuit is analogous to
- Avoltage in an electric circuit
- Bcurrent in an electric circuit
- Cpower in a electric circuit
- Dresistance in a electric circuit
25The unit of magnetic flux is
- Atesla
- Bweber
- Campere-turn
- Dampere-turns/weber
26The unit of magneto-motive force is the
- Atesla
- Bweber
- Campere-turn
- Dampere-turns/ weber
27The unit of flux density is the
- Atesla
- Bweber
- Campere-turn
- Delectron-volt
28The electromagnetic activation of a movable shaft is the basis for
- Arelays
- Bcircuit breakers
- Cmagnetic switches
- Dsolenoids
29When there is current through a wire placed in a magnetic field,
- Athe wire will overheat
- Bthe wire will become magnetized
- Ca force is exerted on the wire
- Dthe magnetic field will be cancelled
30A 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
- Aremain unchanged
- Bdecrease
- Cincrease
- Dbe excessive
31if a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage induced in the conductor will
- Aremain constant
- Breverse polarity
- Cbe reduced
- Dbe increased
32In the crankshaft position sensor in figure 10-33, the induced voltage across the coil is caused by
- Aa current in the coil
- Brotation of the steel disk
- Ca tab passing through the magnetic field
- Dacceleration of the steel disks rotational speed
33The purpose of the commutator in a generator or motor is to
- Achange the direction of the current to the rotor as it spins
- Bchange the direction of the current to the stator winding's
- Csupport the motor or generator shaft
- Dprovide the magnetic field for the motor or generator
34In a motor, back emf serves to
- Aincrease power from the motor
- Bdecrease flux
- Cincrease the current in the field windings
- Ddecrease the current in the armature
35The torque of a motor is proportional to the
- Aamount of flux
- Barmature current
- Cboth of the above
- Dnone of the above
36The difference between alternating current (AC) and direct current (DC) is
- Aac changes value and dc does not
- Bac changes direction and dc does not
- Cboth answers A and B
- Dneither answers A and B
37During each cycle, a sine wave reaches a peak value
- Aone time
- Btwo times
- Cfour times
- Da number of times depending on the frequency
38A sine wave with a frequency of 12 kHz is changing at a faster rate than a sine wave with a frequency of
- A20 kHz
- B15,000 Hz
- C10,000 Hz
- D1.25 MHz
39A sine wave with a period of 2 ms is changing at a faster rate than a sine wave with a period of
- A1 ms
- B0.0025 s
- C1.5 ms
- D1200 ms
40when a sine wave has a frequency of 60 Hz, in 10 s it goes through
- A6 cycles
- B10 cycles
- C1/16 cycle
- D600 cycles
41if the peak value of a sine wave is 10 V, the peak-to-peak value is
- A20 V
- B5V
- C100V
- Dnone of these
42I the peak value of a sine wave is 20V, the rms value is
- A14.14 V
- B6.37 V
- C7.07 V
- D5 V
43The average value of a 10 V peak sine wave over one complete cycle is
- A0 V
- B6.37 V
- C7.07 V
- D5 V
44The average half-cycle value of a sine wave with a 20 V peak is
- A0 V
- B6.37 V
- C12.74 V
- D14.14 V
45One 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
- A55°
- B35°
- C0°
- Dnone of these
46The instantaneous value of a 15 A peak sine wave point at a 32° from its postive-going zero crossing is
- A7.95 A
- B7.5 A
- C2.13 A
- D7.95 V
47A phasor represents
- Athew magnitude of a quantity
- Bthe magnitude and direction of a quantity
- Cthe phase angle
- Dthe length quantity
48if the rms current through a 10kΩ resistor is 5 mA, the rms voltage drop across the resistors is
- A70.7 V
- B7.07 V
- C5 V
- D50V
49Two 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
- A9.7 V
- B9.19 V
- C13.72 V
- D4.53 V
50An advatage of a three-phase induction motor is that it
- Amaintains constant speed at any load
- Bdoes not require starting winding's
- Chas a wound rotor
- Dall of the above
51The difference in the synchronous speed of the stator field and the rotor speed of the motor is called
- Adifferential speed
- Bloading
- Clag
- Dslip
52a 10kHz pulse waveform consists of pulses that are 10us wide. Its duty cycle is
- A100%
- B10%
- C1%
- Dnot determinable
53The duty cycle of a square wave
- Avaries wit the frequency
- Bvaries with the pulse width
- Cboth answers A and B
- Dis 50%
Información
- Descripción
- Test sobre ELT AC quiz 1-2 , creado por Andrew Best el 18/01/2018.
- Autor
- Andrew Best
- Idioma
- English
- Visitas
- 94
- Historial
- Creado el 18 ene 2018 · actualizado el 18 ene 2018
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