2817962
Descripción
Test por Oliver Balay, actualizado hace más de 1 año
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Creado por Oliver Balay
hace casi 9 años
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Pregunta 1
Pregunta
Electric current is described as a flow of
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protons
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neutrons
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electrons
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nucleus
Pregunta 2
Pregunta
Which one of the following identifies the sources of an electromotive force?
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Atomic, magnetic, thermal
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Chemical, atomic, thermal
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Chemical, magnetic, thermal
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Chemical, magnetic, atomic
Pregunta 3
Pregunta
When the current passing through a conductor is increased, the conductor’s temperature will:
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decrease
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stabilise
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fragment
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increase
Pregunta 4
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capacitance
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inductance
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frequency
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flux density
Pregunta 5
Pregunta
Ohm is the SI unit of measurement for:
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resistance
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voltage
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current
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charge
Pregunta 6
Pregunta
The SI unit for frequency is the
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Joule
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Mole
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Farad
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Hertz
Pregunta 7
Pregunta
Resistance, potential difference and electrical current are expressed in the same order as units of:
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Ohms, Volts, Amperes
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Ohms, Watts, Amperes
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Ohms, Volts, Watts
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Watts, Volts, Ohms
Pregunta 8
Pregunta
Transpose the formula Z² = R² + X² to make R² the subject.
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R² = X² – Z²
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R² = Z² – X²
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R² = Z² + X²
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R² = X² x Z²
Pregunta 9
Pregunta
If the resistivity of aluminium is 2.65 x 10 -8 /metre, the resistance of a 65 metre length of 16mm2 aluminium conductor is:
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10.77Ω
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1.108Ω
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0.0108Ω
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0.108Ω
Pregunta 10
Pregunta
For the circuit shown, the total resistance is:
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108Ω
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36Ω
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12Ω
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3.6Ω
Pregunta 11
Pregunta
For the circuit shown, the power dissipated by the 15Ω resistor is:
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240W
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60W
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160W
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40W
Pregunta 12
Pregunta
The power dissipated in the circuit shown on the right would be:
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35W
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833W
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350W
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1,399W
Pregunta 13
Pregunta
When measuring current flow in a d.c. circuit, an ammeter must be connected:
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using a rectifier
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using a VT
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in series with the load
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in parallel with the load
Pregunta 14
Pregunta
Instrument B in the figure on the right measures the:
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voltage drop caused by R2
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voltage drop caused by R3
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current through R1
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current through R2
Pregunta 15
Pregunta
The strength of the magnetic flux produced when current flows in a conductor can be increased by:
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increasing the current
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decreasing the current
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reversing the current
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using alternating current
Pregunta 16
Pregunta
Which one of the following shows the correct poles of the electromagnet when current flows in the direction shown?
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a)
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b)
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c)
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d)
Pregunta 17
Pregunta
What would be the effect on magnetic flux for the two equal, current-carrying conductors shown?
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The magnetic field would halve in strength, flowing in opposite directions
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The magnetic fields around each of the conductors would rotate independently
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The magnetic fields around the conductors would cancel each other out
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The magnetic field around the conductors would double in strength and flow in the same direction
Pregunta 18
Pregunta
A conductor of a simple alternator is 0.4m long and cuts a magnetic field with a magnetic flux density of 1.5 tesla at a velocity of 30m/s. The EMF induced in the conductor will be:
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1,800V
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180V
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18V
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1.8V
Pregunta 19
Pregunta
Which one of the following is the supply frequency if a sine wave has a periodic time of 20 milliseconds?
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40Hz
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50Hz
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60Hz
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70Hz
Pregunta 20
Pregunta
Refer to the figure shown. What does value A indicate?
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Average value of the waveform
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Periodic time of the waveform
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RMS value of the waveform
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Peak amplitude of the waveform
Pregunta 21
Pregunta
Which one of the following quantities can be described as a force?
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Gravity
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Current
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Resistance
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Energy
Pregunta 22
Pregunta
The formula shown is used to determine the force required given mass and acceleration. Which one of the following would be the acceleration for a mass of 20kg having a force of 10N applied? F = m x a
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200 m/s²
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0.5 m/s²
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5 m/s²
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50 m/s²
Pregunta 23
Pregunta
The power required to raise a mass of 8kg across a distance of 10m in 40 seconds is approximately:
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785W
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80W
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20W
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5W
Pregunta 24
Pregunta
A motor produces an output of 1.2kW when the input is 1.4kW; its efficiency is:
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85.7%
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75.7%
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65.7%
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55.7%
Pregunta 25
Pregunta
When used to ‘inch’ heavy equipment across the floor, a crowbar is being:
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a pulley
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a lift
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a machine
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a lever
Pregunta 26
Pregunta
Which one of the following instruments would be used to measure the line voltage for the star connected load?
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A
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B
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C
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D
Pregunta 27
Pregunta
In a four-wire, three phase system the phase voltage is 220v. The line voltage will be:
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380V
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400V
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415V
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420V
Pregunta 28
Pregunta
Which one of the following is the phase voltage for a star connected load if the line voltage is 400V?
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400V
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230V
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110V
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50V
Pregunta 29
Pregunta
Which one of the following instruments would be used to measure the line current for the delta connected load?
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A
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B
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C
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D
Pregunta 30
Pregunta
The line current feeding a delta load is 52A. The delta phase current will be:
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30A
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52A
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90A
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156A
Pregunta 31
Pregunta
The phase current in a delta load is 10A. The line current will be:
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5A
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5.8A
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10A
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17.3A
Pregunta 32
Pregunta
A balanced three phase star connected load draws a line current of 24A per phase. Which of the following is the approximate value of neutral current?
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0A
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8A
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13.9A
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24A
Pregunta 33
Pregunta
A d.c. motor in which the current remains constant in the field winding but varies in the armature winding is called:
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a compound machine
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an armature machine
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a shunt machine
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a series machine
Pregunta 34
Pregunta
If a single loop of wire connected to a commutator is rotated in a permanent magnetic field, the voltage measured at the commutator will be:
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d.c.
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a.c.
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intermittent
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unidirectional
Pregunta 35
Pregunta
The diagram shows a simple motor, indicating the field poles and direction of current flow. In which one of the following directions would the conductor move?
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Direction A
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Direction B
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Direction C
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Direction D
Pregunta 36
Pregunta
In a 400v to 4,000v step-up transformer the ratio of primary to secondary turns ratio will be:
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10:1
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5:1
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1:5
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1:10
Pregunta 37
Pregunta
Which one of the following components would cause current and voltage to behave as indicated in the sine wave shown?
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Rectifier
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Capacitor
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Inductor
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Resistor
Pregunta 38
Pregunta
The power triangle shown gives the relationship between powers in an a.c. circuit. Which one of the following is the unit used to measure Apparent power?
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kW
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kVA
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kVAr
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kJ
Pregunta 39
Pregunta
A circuit dissipates 3kW at a power factor of 0.7 when connected to a 230V a.c. supply. The current flowing in the circuit will be:
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13.0A
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18.6A
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21.5A
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25.2A
Pregunta 40
Pregunta
Power factor correction in circuits having lagging power factors can be achieved by connecting:
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inductors across the load
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resistors across the load
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resistors in series with the load
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capacitors across the load
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