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ME-175-22-03 > L Theory > Flashcards

L Theory Flashcards

1
Q

What is current?

A

Current is the flow of electrons past a point in one second
1Amp = 6.241x10^18 electrons per second

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2
Q

What are the 6 methods of producing a voltage?

A
  1. chemical
  2. friction
  3. induction
  4. heat
  5. light
  6. pressure
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3
Q

For potential difference to exist between two points a circuit must have a ?

A

A difference in charge.

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4
Q

what is potential difference measured in?

A

Volts(V)

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5
Q

what force is used to push voltage around a circuit?

A

Electromotive Force

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6
Q

To produce a voltage chemically, what must the plates be made of?

A

Dissimilar metals.

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7
Q

what are the 3 requirements for inducing a voltage?

A
  1. a conductor
  2. a magnetic field
  3. relative movement
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8
Q

what determines the polarity of a induced voltage?

A

The direction of movement between the conductor and magnetic field.

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9
Q

what 2 things determines the voltage produced by a thermocouple?

A

1.types of materials used
2.diffrence in temp at both ends

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10
Q

what is the name of the materials used in solar panels?

A

Semiconductors

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11
Q

what materials produce voltage when pressure is applied?

A

piezo quartz crystal

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12
Q

what is the circuit symbol for current?

A

I for intensity

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13
Q

what is current measured in?

A

Amps(A) or Ampere

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14
Q

what is the outer orbit of a atom called?

A

Valance shell.

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15
Q

what is the outer electron called?

A

Valance electron

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16
Q

what is the polarity of a electron?

A

negative

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17
Q

what is the name of the electron that is released form a atom?

A

free electron.

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18
Q

what is the name of a atom that that has released a electron?

A

Positive ion

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19
Q

what is stated in ohms law?

A

That a current flowing through a conductor, is directly proportional to the applied voltage across it, providing that the temperature remains constant, and is inversely proportional to the resistance.

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20
Q

what is the formula for ohms law?

A

Voltage(v)=Current(I)×Resistance(R)

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21
Q

what is a series circuit and its main down fall?

A

A circuit where two or more components are connected end to end.
downfall: one component fails the circuit is broken

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22
Q

how do you find the resistance of a series circuit?

A

add all of the resistances up
Rt = R1+R2+R3
don’t forget your units ohms(Ω)

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23
Q

what happens to current and voltage in a series circuit

A

currant stays constant and voltage changes

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24
Q

what is a parallel circuit?

A

all of the components are connected side by side said to be parallel to each other

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25
Q

what is the formula for total resistance in a parallel circuit.

A

1/Rt=1/r1+1/r2+1/r3 + …

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26
Q

what happens to voltage and currant in a parallel circuit?

A

the voltage is the same in every component but the currant is different for every component.

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27
Q

what is a series parallel circuit?

A

a circuit with components in series and parallel

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28
Q

what part of a series parallel circuit do we calculate first?

A

we start with the parallel section of the circuit so that we can then calculate the rest as a series circuit.

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29
Q

how are ammeters connected in a circuit?

A

a ammeter must be connected in series.

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30
Q

how are voltmeters connected in a circuit?

A

a voltmeter must be connected in parallel.

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31
Q

what is this symbol (µ) when it comes to units?

A

micro 1/1000000 or 0.000001

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32
Q

what is this symbol (m) when it comes to units?

A

milli 1/1000 or 0.001

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33
Q

what is this symbol (k) when it comes to units?

A

kilo 1,000

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34
Q

what is this symbol (M) when it comes to units?

A

Mega 1,000,000

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35
Q

what is this symbol (G) when it comes to units?

A

Giga 1,000,000,00

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36
Q

what is the formula for mechanical power?

A

power = (force x distance)/time

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37
Q

electrical power depends on what two factors?

A
  1. number of electrons being moved (current)
  2. the rate at which they are made to travel (voltage)
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38
Q

what is the formula for electrical power?

A

power = current x voltage

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39
Q

what is the unit for power?

A

watts(W)

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40
Q

how many watts are in a 1 horse power?

A

746 watts

41
Q

what are the two types of resistance values for equipment like lamps and toasters?

A

cold resistance( no voltage applied)
hot resistance (voltage applied)
can be measured using GPTME fluke or MIT instrument set on the ohms scale

42
Q

what does passing a current through a conductor produce?

A

heat and a magnetic field

43
Q

why are fuses important?

A

to protect the supply as if the equipment is drawing more then the fuse rating it already has a issue.

44
Q

what are the two different types of fuses

A
  1. cartridge(normal domestic fuse)
    2.high rupturing capacity(quartz powder)
45
Q

what is the potential difference of the sea?

A

0 volts.

46
Q

what is the resistance of a human?

A

1000 ohms

47
Q

why do we earth all equipment and what is the highest allowed resistance of a earth point?

A

earthing is there to protect us from electric shock as it is the easiest route at 0.1ohms.

48
Q

what are the 3 main causes of earth faults?

A
  1. Dampness
  2. hard or brittle insulation
  3. accidental damage
49
Q

what will two earths do in a circuit?

A

by pass components and lower the resistance and increase the currant leading to possible damage.

50
Q

how is a magnetic force induced?

A

by passing a current through a conductor

51
Q

what are temporary magnets

A

magnets that have there forces induced by a current or another magnet

52
Q

what do poles of the same type do ?

A

they repel each other

53
Q

what can be added to steel to produce a stronger magnet

A

nickel
cobalt
aluminium

54
Q

what is the right hand grip rule?

A

thumb points in direction of current flow
fingers wrap round the conductor to show the magnetic field.

55
Q

what is the normal supply on a boat?

A

3 phase 450v 60hertz

56
Q

how many times does a sine wave reach peak?

A

twice once positive and once negative in one cycle

57
Q

what does a coil of wire make?

A

a basic inductor.

58
Q

what is self inductance?

A

when AC flows through a coil an alternating magnetic field is generated around the coil creating a EMF

59
Q

what is mutual inductance?

A

when EMF is generated in a second coil

60
Q

why do we use a soft iron core in transformers?

A

to allow the magnetic flux to reach the secondary coil as soft iron is better then air at transferring magnetic flux.

61
Q

what is the purpose of a transformer?

A

to step voltage up or down depending on its windings.

62
Q

what are the the two types of transformer?

A
  1. core type
  2. shell type
63
Q

what will happen to the voltage when the secondary coil has twice as many windings as the primary coil?

A

the voltage will step up to double the input voltage in the primary coil.

64
Q

do transformers work with DC?

A

no because DC only creates a change in magnetic field when it is turned off or on.

65
Q

why do we use a laminated core rather then just a block of soft iron in transformers?

A

as the resistance of a block is low allowing for more Eddie currants which would counteract the magnetic flux from the induced coil.

66
Q

How are input cables ladled for 3 phase?

A

red L1
yellow L2
blue L3

67
Q

how are output cables ladled for 3 phase?

A

red A
yellow B
blue C

68
Q

what are the six parts of a brushless AC generator?

A

prime mover
high frequency generator
automatic voltage regulator
AC exciter generator
rectifier assembly
main AC generator

69
Q

what does generated voltage depend on?

A

strength of the magnetic field and the amount of the field that cut the conductors

70
Q

what is the most common generator?

A

AC brushless generator

71
Q

what does AVR stand for and why is it important?

A

Automatic Voltage Regulator
it is used to power the exciter stators with DC and senses the power output from the AC generator stators

72
Q

why do we need the exciter parts of a AC brushless generator?

A

so that we can provide the generator rotor with AC for the rectifier assembly

73
Q

what are the advantages of AC motors?

A
  1. less maintenance
  2. smaller for same power as DC
74
Q

what is the most common AC motor

A

AC induction motor (squirrel cage induction motor)

75
Q

what are the two main components of a motor?

A

stator and rotor

76
Q

what is the polarity of a rotor compared to the stator?

A

opposite so that its magnetic field is attracted to the stators magnetic field causing the rotor to turn.

77
Q

what two things determine the torque of a DC motor.

A

1.magnitude of the armature current.
2.strength of the magnetic field of the field windings

78
Q

how do you remember the left hand rule.

A

First Finger = magnetic Field
seCond finger = direction of Current
thuMb = Movement

79
Q

what is back EMF?

A

EMF induced that opposes the main EMF.

80
Q

what are the 3 categories of DC motor?

A

series
shunt (parallel)
compound (mix of series and parallel

81
Q

what are the characteristics of a series motor

A

good starting torque
poor speed control
slow with heavy loads rapid with light loads
always need a load or will be damaged
field winding in series with armature

82
Q

what are the characteristics of a shunt motor

A

field windings in parallel with armature
many turns of thin gauge wire
poor starting torque
good regulation under load
torque develops with armature current
constant speed

83
Q

what are the characteristics of a compound motor?

A

best of both motors
good torque Characteristics
good speed regulation

84
Q

what is a geometrical neutral axis?

A

neutral axis between field windings

85
Q

what is a magnetic neutral axis?

A

a axis that moves with the distortion of the field winding magnetic field.

86
Q

what are interpoles used for?

A

they are opposite in polarity to the next pole in the rotation to offset varying armature current and assist rotation.

87
Q

What holds the electrons in the atom?

A

Force of Attraction

88
Q

why do we use centre tapped transformers?

A

to reduce the potential electric shock by half if the cable becomes damaged. 115v to 57.5V

89
Q

how can AC induction motors be wound

A

Star
Delta

90
Q

what is the name of the natural magnetic iron ore?

A

Magnetite

91
Q

what are the 2 most common permanent magnets?

A
  1. bar
  2. horseshoe
92
Q

speed at which AC changes direction is called?

A

Frequency

93
Q

the level to which the voltage or current rises to is called ?

A

Amplitude

94
Q

how are AC cycles per second expressed?

A

Hertz

95
Q

what is the unit for inductance?

A

Henry’s

96
Q

what is the frequency equation?

A

time (seconds) = 1/ frequency

97
Q

what are the two type of transformers?

A

1 core
2 shell

98
Q

what are the new colours for 3 phase

A

Brown L1 A
Black L2 B
Grey L3 C

ME-175-22-03 (15 decks)

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