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175/22/02 > L Theory > Flashcards

L Theory Flashcards

1
Q

What holds the electron in orbit around the nucleus

A

Force of attraction

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2
Q

What is the outer obit of an atom called

A

Valance shell

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3
Q

What is the polarity of an electron

A

Negative

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4
Q

If an electronic is removed from the atom, what is the electron called?

A

Free electron

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5
Q

If an electron is removed from a balanced atom, what is the stomach now know as

A

Positive ion (positively charged)

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6
Q

Electrical flow is always ….

A

Negative to positive(-ve to +ve)

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7
Q

If current was to flow from positive to negative(+ve to -ve) what is it called

A

Conventional current flow

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8
Q

What is the symbol for current

A

I

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9
Q

What is current measured in

A

Amps

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10
Q

What is the electron called that is in the outer orbit of the atom

A

Valance electron

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11
Q

Potential differnce will exist between two points in a circuit will have a …..

A

Difference in charge

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12
Q

What is potential difference is measured in?

A

Volts

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13
Q

What is the force that drives current round a circuit

A

Voltage

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14
Q

Name 6 methods that can produce voltage

A

Induction heat
Friction pressure
Light chemical

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15
Q

To produce voltage in a chemically, what do the different plates need to be made of?

A

Different metals

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16
Q

Give an example of creating voltage using friction

A

Rubbing socks on a carpet

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17
Q

Name 3 requirements for induction voltage

A

Relative movement
Magnetic field
Electrical conductor

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18
Q

What determins the polarity of induced voltage

A

The movement of the conductor through the magnetic field

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19
Q

What determines the voltage in a thermocouple

A

The differnce in temperature and the matrial used

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20
Q

What is used in solar panels

A

Semiconductor

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21
Q

A material with many free electrons will pass current freely is called a…

A

Conductor

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22
Q

List at least 4 examples of conductors

A

Copper
Gold
aluminium
Steel
Carbon

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23
Q

A material with few free electrons and can only pass with difficulty is called an….

A

Insulator

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24
Q

Give at last 4 examples of insulators

A

Plastic
Fabric
Paper
Rubber
Glass

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25
Q

List 4 examples of what could cause resistance in a circuit

A

Heat
Cross face area
Length
Type of material

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26
Q

State ohms law

A

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

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27
Q

What is resistance measure in

A

Ohms

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28
Q

What is the formula for total resistance in a series circuit

A

Rt= R1+R2+R3

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29
Q

What is the equation for total resistance in a parallel circuit

A

RT=1/R1+1/R2+1/R3

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30
Q

Define electrical power

A

The rate of doing work
Power=(force×distance)÷time

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31
Q

What is the unit for power

A

Watts

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32
Q

How many Watts makes 1HP

A

746W

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33
Q

What’s the danger of passing constant high current through a conductor

A

Can overheat and cause a electrical fire

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34
Q

Name two types of fuses

A

High Rupturing Capacity(HRC)
Cartridge Fuse

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35
Q

What does the fuse protect

A

The power source

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36
Q

What happens to a HRC fuse when it blows

A

The powder covers and solidifies over the broken contacts and this prevents it from completing the circuit

37
Q

What is the electrical potential of the sea

A

0volts

38
Q

3 things that can cause a earth fault

A

Dampness
Accidental damage
Insulation becoming brittle with age or heat

39
Q

Why is equipment earthed to the ships hull

A

Because the Hull is at earth potential thus 0 volts meaning someone standing on earth cannot be shocked from touching casing

40
Q

What is the name of the natural magnetic ore

A

Magnetite

41
Q

What direction do lines of magnetic flux travil

A

North to South
Negative to positive

42
Q

List at least 3 materials mixed with steel, will produce stronger magnetics

A

Copper
Iron
Nickle
Cobalt
Aluminium

43
Q

What is produced around a conductor passing current

A

Magnetic field
Heat

44
Q

Permanent and electro-magnet are two ways of producing magnets what’s the third

A

Temporary magnet

45
Q

List 2 advantages of AC over DC

A

Can transformed to get a range of voltage via a transformer
Equipment is usually lighter

46
Q

At what speed is ac changing direction called(measured in)

A

Frequency

47
Q

The level to which the voltage raises to in an ac wavelength graph

A

Peak value

48
Q

How are AC cycles expressed(unit of measurement)

A

Hertz

49
Q

What are the values of the ships electrical supplies draw

A

450V
60Hz
3 phase

50
Q

Draw the frequency equation

A

(Seconds)
Time= 1
Frequency

51
Q

What is the unit of inductance and what are the more common values

A

Henry
Milli Henry
Micro Henry

52
Q

Label all parts of ac waveform

A

One cycle
+peak value
-Peak value
Amplitude
Time axis

53
Q

Will a transformer work with dc current

A

No

54
Q

Why won’t dc work with a transformer

A

They only work with AC as it is always changing which gives us our relative movement

55
Q

Name two types of transformers

A

Shell
Core

56
Q

What is the purpose of a transformer

A

To either increase or decrease the voltage

57
Q

What is the purpose of a laminated soft iron core

A

It passes the magnetic field and voltage from one coil with another

58
Q

State the output voltage equation

A

Output. No. of secondary coils
= ×input volts
Volts. No. Of primary coils

59
Q

Purpose of a centre tapped transformer

A

Has an earth centre in the secondary coil, which half’s the voltage
This reduces the shock effect by half

60
Q

Identify the input and output cables on hm ships

A

Input. Output
Red- L1. A
Yellow- L2. B
Blue. - L3. C

61
Q

What are the new colour codes

A

Red is now brown
Yellow is now black
Blue is now gray

62
Q

What the most common type of generator today

A

Brushless generator

63
Q

2 things EMF output depends on

A

1)Amount of lines of force cutting across the conductor as they rotate
2) the speed the generator is rotating

64
Q

How is the HF generator turned

A

Is belt driving, its output is 115volts

65
Q

What current is fed to the exciter stator

A

Direct current

66
Q

What is the purpose of the rectifier assembly

A

Converts ac output to DC for the main generator rotors

67
Q

If the magnetic field around the around the ac generator is stable(made from DC supply) how does the generator produce ac output

A

The last generator produces an AC output as the rotor rotates round 3 AC stator, producing 3 Phase AC current

68
Q

What is the output from generators on hm ships and how does the AVR know what’s being produced

A

450V
60 hertz
3 phase
It is connected to the 3 phase by a sensing line

69
Q

Lists 4 advantages of AC motors

A

Less maintenance
More efficient than smaller dc motors
Cheaper than DC
More compact

70
Q

What is the main disadvantage of an AC motor

A

Needs specialist equipment to vary speed

71
Q

List the 2 main components of a AC motor

A

The stator
The rotor

72
Q

What causes the movement in a 3-phase induction motor

A

Rotating magnetic field

73
Q

What is the most common type of AC motor used on hm ships

A

Squirrel cage induction motor

74
Q

List the components of a squirrel motor
(4)

A

Copper end ring
Drive end bearing
No drive end bearing
Copper bars

75
Q

How does the rotating magnetic field from the stator cause rotor to rotate

A

It has the opposite polarity of the stator magnetic field, and the interaction of the two fields causes the rotor to turn to follow the rotating field

76
Q

Why are there less maintenance on a AC motor

A

There is no electrical connection(carbon contacts) meaning you don’t need brushes and slip rings, simplifying construction and less parts to wear

77
Q

What would happen to a running 3 phase motor if it lost 1 phase

A

It would start vibrating and loose power and start overheating

78
Q

If a shutdown 3 phase motor looses 1 of its phases what affect would this have

A

It wouldn’t start

79
Q

What is the DC motor generally made from

A

Coils of wire

80
Q

What does maxwell right and grip indicates

A

Direction of the magnetic field around the conductor

81
Q

What will lines of magnetic flux never do

A

Cross

82
Q

Using flaming left hand rule.
What does each digit indicate

A

Thumb= motion
First finger= field
Second finger= current

83
Q

What is back EMF

A

Is the emf created by the generator that flows in a differnt direction to the EMF.

84
Q

What is The amount of torque produced dependant on(2)

A

Strength of the magnetic field
Magnitude of the armature current

85
Q

List 3 classifications of DC motors(type)

A

Series wound
Shunt wound
Compound wound

86
Q

Why must the carbon brushes fixed in the same position as and why

A

The must be fixed directly opposite along the magnetic neutral axes and this is to prevent any back EMF

87
Q

Describe armature reaction

A

A magnetic field is created around the armature. The armature magnetic field will distort the winding magnetic field

88
Q

What are inter-poles and where are they positioned and why

A

Inter-poles are similar poles just smaller.
They are placed between the main poles and wound in series with the armature.
They neutralise the effect of armature reaction

175/22/02 (1 decks)

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