B1-3 Electricity Flashcards Preview

Unit Tests > B1-3 Electricity > Flashcards

Flashcards in B1-3 Electricity Deck (71)
0
Q
```If 100 meters of a certain wire 1mm in diameter has a resistance of 2 ohms, calculate the resistance of 2 km of the same wire passing the same current.
A) 80 ohms
B) 40 ohms
C) 20 ohms
D) 1.0 ohms
E) 0.1 ohms```
A

B) 40 ohms

1
Q
```An electric motor has an output shaft power of 7.5 kW, and draws a current of 40 amps from a 220 volt circuit. Its efficiency is:
A) 92.7%
B) 87.5%
C) 85.8%
D) 85.2%
E) 75.2%```
A

D) 85.2%

2
Q
```The power that would be dissipated by a resistor with a supply voltage of 120 volts DC and a current of 8 amperes is:
A) 960 watts
B) 960 ohms
C) 15 watts
D) 15 ohms
E) 0.067 watts```
A

A) 960 watts

3
Q
```Three resistances of 20, 50 and 80 ohms make up a series circuit. Supply voltage is 400 volts. The current flowing would be:
A) 33.0 amps
B) 8.0 amps
C) 5.47 amps
D) 2.67 amps
E) 0.375 amps```
A

D) 2.67 amps

4
Q
```Three resistors of 20 ohms, 60 ohms and 120 ohms are connected in parallel to an electrical supply. Current through the circuit is 60 A. The applied voltage is:
A) 12,000 volts
B) 7,200 volts
C) 800 volts
D) 13.33 volts
E) 1.33 volts```
A

C) 800 volts

5
Q
```The unit of measurement for e.m.f. Is the:
A) ampere
B) hertz
C) volt
D) ohm
A

C) volt

6
Q

To increase the voltage developed by a conductor moving through a magnetic field:
A) decrease the resistance of the conductor
B) decrease the number of loops of wire in the rotor which is producing the electric current
C) increase the diameter of the loos in the rotor which is producing the electric current
D) increase the strength of the magnetic field
E) increase the resistance of the conductor

A

D) increase the strength of the magnetic field

7
Q
```If a conductor is moved across a stationary magnetic field, it forms what is known as:
A) conduction
B) electromagnetism
C) transformer action
D) generator action
E) motor action```
A

D) generator action

8
Q
```In a DC generator, commutation is the process of converting AC to:
A) heat
B) power
C) resistance
D) direct current
E) voltage```
A

D) direct current

9
Q

When a conductor is moved and cuts magnetic flux lines at an angle of 90 degrees:
A) motor action will be experienced
B) voltage generated will be at maximum
C) maximum resistance to current flow will result
D) current flow has the least resistance
E) armature rotation will have the least resistance

A

B) voltage generated will be maximum

10
Q
```The minimum voltage generated by a single loop DC generator occurs when the conductor cutting the magnetic lines of forces at an angle of:
A) 45 degrees
B) 90 degrees
C) 120 degrees
D) 180 degrees
E) 270 degrees```
A

D) 180 degrees

11
Q
```Components of the kWh meter include (4 correct answers):
A) a current coil
B) clamping jaws
C) a voltage coil
D) a registering mechanism
E) a compensating coil```
A

A) a current coil
C) a voltage coil
D) a registering mechanism
E) a compensating coil

12
Q
```The potential difference between two points in an electrical circuit is measured by a:
A) piezometer
B) ohmmeter
C) ammeter
D) wattmeter
E) voltmeter```
A

E) voltmeter

13
Q

A power meter:
A) consists of a voltage coil, a compensating coil, a revolving disc and a registering mechanism only
B) usually registers a value proportional to the actual load that is adjusted using a multiplier number
C) reads always the actual power consumed
D) is read from left to right. Has dials all spinning clockwise
E) has dials all spinning clockwise

A

B) usually registers a value proportional to the actual load that is adjusted using a multiplier number

14
Q
```The black demand pointer of a power meter:
A) must be manually reset
B) always reads the current demand
C) indicates the amperage being drawn
D) resets automatically
E) moves the red pointer```
A

A) must be manually reset

15
Q

A kilowatt hour meter has a small motor which:
A) moves the meter demand pointer
B) has a speed proportional to power consumption
C) indicates the multiplier to be used when reading the meter
D) slows down as power consumption increases
E) turns at a constant speed

A

B) has a speed proportional to power consumption

16
Q
```A megohmmeter measures:
A) current flow
B) voltage drop
C) resistance
D) megawatts of power
E) amperage```
A

C) resistance

17
Q

In a series wound DC generator:
A) there are no field poles
B) the shunt winding taps in before the series winding
C) the shunt winding taps in after the series winding
D) load current passes through the field windings
E) the field poles are perforated for cooling

A

D) load current passes through the field windings

18
Q
```A common use for a DC generator is:
A) power factor correction
B) computer room power supply
C) power supply for portable welder machines
D) power supply for a machinists lathe
E) an automobile alternator```
A

C) power supply for portable welding machines

19
Q
```Utility companies have a surcharge to their customers based on:
A) low usage frequency
B) a poor power factor
C) low transformer efficiency
D) the maximum amperage used
E) the maximum voltage used```
A

B) a poor power factor

20
Q
```A commutator would be found in:
A) an AC generator
B) a synchronous motor
C) a wound rotor motor
D) an induction motor
E) a DC generator```
A

E) a DC generator

21
Q
```Alternators must run at constant speed in order to maintain correct:
A) rotor resistance
B) output power
C) field current
D) frequency
E) field voltage```
A

D) frequency

22
Q
```The \_\_\_\_\_\_ of a DC machine is built up of laminated plates mounted on the shaft. The coils are connected to a commutator mounted on one end of the rotor shaft.
A) stator
B) armature
C) rheostat
D) coils
E) yoke```
A

B) armature

23
Q
```The purpose of an electrical transformer is to change:
A) DC from one voltage to another
B) DC from one amperage to another
C) AC from one wattage to another
D) DC from one resistance to another
E) AC from one voltage to another```
A

E) AC from one voltage to another

24
Q

An active current transformer should never:
A) be inspected until properly grounded
B) have its secondary connected to a meter
C) have its primary circuit open
D) have its secondary circuit open
E) produce excessively high voltages

A

D) have its secondary circuit open

25
Q
```Some of the hazards of electrical transformer cooling oil can be compensated for by adding:
A) organic compounds
B) freon
C) chlorinated hydrocarbons
D) anti foaming substances
E) chelates```
A

C) chlorinated hydrocarbons

26
Q
```If the primary and secondary voltages of a transformer are 220 V and 1100 V respectively, and the primary has 3000 turns, how many turns does the secondary have?
A) 600
B) 1100
C) 1320
D) 6000
E) 15000```
A

E) 15000

27
Q
```Major losses that occur in a transformer include copper losses, eddy current losses and:
A) magnetic hysteresis losses
B) capacitive current generation losses
C) capacitance losses
D) self inductance losses
E) flux leakage losses```
A

A) magnetic hysteresis losses

28
Q
```A step down transformer has 600 turns on the primary winding. It is required that the voltage be lowered from 120 V to 12 V. The number of turns on the secondary winding must be:
A) 2.4
B) 5.0
C) 60
D) 540
E) 6000```
A

C) 60

29
Q
```In a 120/240 V one phase, three wire circuit, the colour of the circuit conductor that is grounded is:
A) white
B) black
C) red
D) green
E) blue```
A

A) white

30
Q
```In a 120/240 V, single phase, three wire circuit, the colours of conductors are: (select 3 correct answers)
A) white
B) blue
C) red
D) black
E) green```
A

A) white
C) red
D) black

31
Q
```A prime factor in determining the voltage to be used in an electrical circuit is:
A) transformer capacity
C) peak demands
D) the resistance of the circuit
E) the number of motors involved```
A

32
Q
```Electrical voltage systems may have an acceptable voltage variation of plus or minus:
A) 10%
B) 7.5%
C) 5%
D) 1.5%
E) 0%```
A

C) 5%

33
Q
```The best type of diagram for showing electrical supply and distribution systems is the:
A) terminal and connection diagram
B) elementary diagram
C) process diagram
D) piping diagram
E) single line diagram (one line)```
A

E) single line diagram (one line)

34
Q
```In a plant electrical distribution system, the electric utility responsibility will not go beyond the:
A) primary transformer
B) motor control centre
C) first trunk circuit
D) first branch line
E) first over current device```
A

C) first over current device

35
Q
```The resistance in a 480 volt circuit which transfers 5.76 kilowatts of power is:
A) 83.33 ohms
B) 40 ohms
C) 2.765 ohms
D) 2765 ohms
E) 12 ohms```
A

B) 40 ohms

36
Q
```The equivalent resistance of several electrical resistors is less:
A) when voltage is decreased
B) when the resistors are in parallel
C) if the amperage is increased
D) when the resistors are in series
E) when a circuit is opened```
A

B) when the resistors are in parallel

37
Q
```A current of 10 amperes flows through a circuit when a voltage of 220 V is applied. The wire in this original circuit is to be replaced with new wire of twice the diameter. The resistance of the new circuit is:
A) 5.5 ohms
B) 11 ohms
C) 22 ohms
D) 44 ohms
E) 110 ohms```
A

A) 5.5 ohms

Although I firmly believe the answer to be B) 11 ohms. Must check on it.

38
Q
```Three resistors of 20 ohms, 60 ohms, and 120 ohms are connected in parallel to an electrical supply. Current through the circuit is 60 amps. The applied voltage is:
A) 12000 V
B) 7200 V
C) 800 V
D) 13.33 V
E) 1.33 V```
A

C) 800 V

39
Q
```10 meters of wire of uniform cross sectional area has a resistance of 20 ohms. If the length of the wire is increase to 500 meters, the resistance will be:
A) 1000 ohms
B) 250 ohms
C) 25 ohms
D) 4.0 ohms
E) 0.4 ohms```
A

A) 1000 ohms

40
Q
```A basic law of electricity is, unlike charges attract each other and like charges:
A) impact each other
B) hold each other
C) attract each other
D) are neutralized
E) repel each other```
A

E) repel each other

41
Q

A conductor supplied with current while in a magnetic field will:
A) have a current induced in it
B) tend to remain stationary
C) want to move with the flux lines
D) tend to move at right angles to the flux lines
E) form a solenoid field circuit

A

D) tend to move at right angles to the flux lines

42
Q

Current flow direction and intensity will:
A) affect magnetic field direction and intensity
B) affect the voltage
C) affect the resistance of a circuit
D) not affect electromagnetic field direction
E) not affect electromagnetic field intensity

A

A) affect magnetic field direction and intensity

43
Q
```The major difference between an AC and a DC generator is that a DC generator has:
A) a rotor
B) a commutator
C) slip rings
D) a field
E) a set of anti friction bearings```
A

B) a commutator

44
Q
```When magnetic flux lines travel and meet in opposing directions, the result can be:
A) generator action
B) electromagnetism
C) solenoid action
D) motor action
E) reluctance```
A

D) motor action

45
Q

To increase the voltage developed by a conductor moving through a magnetic field:
A) decrease the strength of the magnetic field
B) increase the resistance of the conductor
C) increase the number of loops of wire in the rotor which is producing the electric current
D) increase the diameter of the loops in the rotor which is producing the electrical current
E) decrease the resistance of the conductor

A

C) increase the number of loops of wire in the rotor which is producing the electric current

46
Q
```A measure of the ability of a material to conduct magnetic flux is called:
A) magnetomotive force
B) resistive force
C) force of flux
D) permeability
E) flux density```
A

D) permeability

47
Q
```Utility companies have a surcharge to their customers based on:
A) maximum voltage fluctuations each day
B) the maximum frequency encountered
C) peak demand during a billing period
D) low transformer efficiency
E) low usage frequency```
A

C) peak demand during a billing period

48
Q
```The most common measurement made with a meter is:
A) amperage
B) wattage
C) resistance
D) voltage
E) capacitance```
A

D) voltage

49
Q

A power meter:
A) reads always the actual power consumed
B) usually registers a value proportional to the actual load that is adjusted using a multiplier number
C) is read from left to right
D) has dials all spinning clockwise

A

B) usually registers a value proportional to the actual load that is adjusted using a multiplier number

50
Q

Components of the power meter include: (4 correct answers)

1) a voltage coil
2) a current coil
3) a compensating coil
4) clamping jaws
5) a registering mechanism

A

1) a voltage coil
2) a current coil
3) a compensating coil
5) a registering mechanism

51
Q
```DC ammeters are connected with the negative, or black lead, connected to the:
A) positive side of the circuit
B) negative side of the circuit
C) neutral side of the circuit
D) red lead of the meter
E) ground```
A

B) negative side of the circuit

52
Q
```The black demand pointer of a power meter:
A) moves the red pointer
B) always reads the current demand
C) resets automatically
D) indicates the amperage being drawn
E) must be manually reset```
A

E) must be manually reset

53
Q

In a series wound DC generator:
A) the shunt winding taps in after the series winding
B) the field poles are perforated for cooling
C) there are no field poles
D) load current passes through the field windings
E) the shunt winding taps in before the series winding

A

D) load current passes through the field windings

54
Q

In a DC motor, the “counter emf”, or “back electromotive force” is directly proportional to:
A) the armature current
B) the field strength and the armature speed
C) the impressed voltage and the field resistance
D) the square of the armature current
E) the square of the armature speed

A

B) the field strength and the armature speed

55
Q
```Utility companies have a surcharge to their customers based on:
A) the maximum voltage used
B) the maximum amperage used
C) a poor power factor
D) low transformer efficiency
E) low usage frequency```
A

C) a poor power factor

56
Q
```Apparent power is the power:
A) generated by rotating equipment
B) supplied to the electrical system
C) used for the actual work
D) caused by system capacitance
E) resulting from system inductance```
A

B) supplied to the electrical system

57
Q

A rheostat, or voltage regulator, of a DC shunt wound generator is used to:
A) regulate the current to the load
B) regulate the speed of the generator
C) regulate the strength of the electromagnetic field
D) change the AC to DC
E) change the unit into a DC motor

A

C) regulate the strength of the electromagnetic field

58
Q
```An AC motor which operates at all loads at exactly the same speed as the electrical frequency is:
A) a series motor
B) an induction motor
C) a wound rotor induction motor
D) a slip ring motor
E) a synchronous motor```
A

E) a synchronous motor

59
Q
```The purpose of an electrical transformer is to change:
A) AC from one wattage to another
B) DC from one resistance to another
C) AC from one voltage to another
D) DC from one amperage to another
E) DC from one voltage to another```
A

C) AC from one voltage to another

60
Q
```Some of the hazards of electrical transformer cooling oil can be compensated for by adding:
A) chelates
B) anti foaming substances
C) chlorinated hydrocarbons
D) freon
E) organic compounds```
A

C) chlorinated hydrocarbons

61
Q
```The use of electronic switches can result in excessively high transformer voltages due to a phenomenon called:
A) capacitive reactance
B) inductive reactance
C) phase lag
D) reactive voltage loss
E) harmonic distortion```
A

E) harmonic distortion

62
Q
```Major losses that occur in a transformer include copper losses, eddy current losses, and:
A) self inductance losses
B) magnetic hysteresis losses
C) capacitive current generation losses
D) capacitance losses
E) reactance losses```
A

B) magnetic hysteresis losses

63
Q
```An electrical transformer works on the principle of:
A) reverse polarity
B) electromagnetic induction
C) DC power flowing in one direction
D) straight polarity
E) commutation```
A

B) electromagnetic induction

64
Q
```If the primary and secondary voltages of a transformer are 220 V and 1100 V respectively, and the primary has 3000 turns, how many turns does the secondary have?
A) 600
B) 1100
C) 1320
D) 6000
E) 15000```
A

E) 15000

65
Q
```The ability of an electrical circuit to store a charge of electricity, even after the circuit is opened, is called:
A) capacitance
B) hysteresis
C) grounding
D) reactance
E) inductance```
A

A) capacitance

66
Q
```A typical extra low voltage electrical device would be:
A) an aquarium pump
B) a toaster
C) a doorbell
D) a dry cell battery charger
E) a night light```
A

C) a doorbell

67
Q
```In an electrical distribution system, if one source is lost, power can still be maintained to the switchboard main bus by means of:
A) a transformer tap
B) a bus duct
C) a cable tap
D) a fusible panel board
E) a tie breaker```
A

E) a tie breaker

68
Q
```The best type of diagram for showing electrical supply and distribution systems is the:
A) process diagram
B) single line diagram (one line)
C) elementary diagram
D) piping diagram
E) terminal and connection diagram```
A

B) single line diagram (one line)

69
Q
```A plant electrical distribution system is composed of service, feeders and:
A) secondary circuits
B) primary circuits
C) branch circuits
D) trunk circuits
E) underground circuits```
A

C) branch circuits

70
Q
```When working with high voltage electrical systems, the minimum safe distance of approach should be:
A) 5 meters
B) 3 meters
C) 2 meters
D) 1 meter
E) 0.5 meters```
A

C) 2 meters