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P2 - Physics > Current and Mains Electricity > Flashcards

Current and Mains Electricity Flashcards

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1
Q

How are voltmeters always connected?

A

In parallel

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2
Q

If an insulating material gains electrons what happens? Eg?

A

Negatively charged

Eg polythene rod

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3
Q

If an insulating material loses electrons what happens? Example?

A

It becomes positively charged eg Perspex rod

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4
Q

When do insulting materials come charged?

A

When rubbed together because electrons are transferred from one material to another

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5
Q

Features of a series circuit?

A

Dame current across each component
Adding the potential differenc gives the total
Sum of resistance = total resistance

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6
Q

Features of a parallel circuit?

A

Sum of the currents = total current
Potential difference is the same
The bigger the resistor the smaller the current

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7
Q

When would an appliance be doubly insulated?

A

When it has a plastic case

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8
Q

How many milliamps are equal to one amp?

A

0.001 amp

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9
Q

What does reversing the current do?

A

Reverse the voltage

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10
Q

When does the resistance of a filament lamp increase?

A

As the temperature increases

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11
Q

Why are socks and plug cases made of stiff plastic materials?

A

Because it is a good electrical insulator

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12
Q

Why does a resistor become hot when an electrical charge flows through it?

A

Energy trad ferret to the resistor makes it hot

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13
Q

Why are electrical faults dangerous?

A

Can cause electric shocks and fires

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14
Q

How are ammeters always connected?

A

In series

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15
Q

What unit is potential difference?

A

VoLTs

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16
Q

What is the frequency of the mains electricity supply in the UK?

A

50 Hz

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17
Q

Unit of charge?

A

Coulombs

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18
Q

Advantage of putting an insulating sleeve on a water tank?

A

Water stays hotter for longer
Heat for less time
Cost soon recovered

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19
Q

Advantage of hydroelectric power?

A

Can store energy for later use

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20
Q

With the same amount of fossil fuels, how can you reduce the amount of negative effects of burning fossil fuels?

A

Plant trees

Carbon capture

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21
Q

What happens when you run a perspex rod with a dry cloth?

A

Transfers electrons from the surface atom of the rod on to the cloth

Perspex rod becomes positively charged as it loses electrons

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22
Q

What happens when you rub a polythene rod with a dry cloth?

A

Transfers electrons to the surface atoms of the rod on to the cloth
So the polythene rod becomes negatively charged (as the rod gains electrons )

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23
Q

What is charge measured in?

A

Coulombs C

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24
Q

What’s currents measured in?

A

Amps (A)

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25
Q

What does a battery consist of?

A

Two or more cells connected together

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26
Q

What is resistance in?

A

Ohms

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27
Q

In a series circuit what is the current?

A

The same in each component

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28
Q

For a series circuit what is the potential difference?

A

It is found when adding up all of the potential differences

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29
Q

What is the current in a parallel circuit?

A

The sum of all the currents through the separate components

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30
Q

In a parallel circuit what is the pd?

A

The same across each component

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31
Q

What is peak voltage of an alternation potential difference?

A

Maximum voltage measured from 0 volts

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32
Q

What is a neutral wire at?

A

0 volts

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33
Q

What does the live wire do?

A

Alternates in every cycle between positive and negative

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34
Q

What happens when insulating materials are rubbed against each other?

A

They become electrically charged

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35
Q

What happens when two electrically charged objects are brought together?

A

They exert force on each other

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36
Q

What is electric current?

A

The flow of electric charge

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37
Q

What is the SIZE of the electric current?

A

The RATE of the flow of electric charge

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38
Q

What is the definition of potential difference between two points in an electrical circuit?

A

The energy transferred per coulomb of charge that passes between the points

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39
Q

What do current- potential difference graphs show?

A

How the current through a component varies with the potential difference across it

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40
Q

When does the resistance of a filament bulb increase?

A

As the temperature of the filament increase

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41
Q

Why is there increased use of LEDs?

A

Much smaller current than other forms of lighting

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42
Q

When does the resistance of a light dependent resistor decease?

A

As light intensity increase

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43
Q

When does an LED emit light?

A

When a current flows through it in a forward direction

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44
Q

What direction does the current in a diode flow?

A

On only one direction

The diode has very high resistance in th reverse direction

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45
Q

How can you find the resistance of a components?

A

By measuring the current through
And the potential difference across
The component

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46
Q

What is current through a resistor directly proportional to?

At a constant temperature

A

The potential difference across the resistor

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47
Q

What does current depend on?

A

Resistance

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48
Q

The greater the resistance the ____ the current?

For a given potential difference

A

Smaller the current

49
Q

How can you work out the potential difference for cells in series?

A

The sum of the potential difference of each cell

Depending on direction

50
Q

What is the rule for: resistance, current and potential difference

In SERIES

A
  • resistance is the sum of the resistance of each component
  • same current though each component
  • total potential difference is shared between the component
51
Q

What is the rule for: current and potential difference

In PARALLEL

A
  • same potential difference

- total current is the sum of the currents across each component

52
Q

What is an alternating current?

A

A current that is constantly changing direction

53
Q

What is the frequency of the U.K. mains supply?

A

50 Hz

54
Q

What is the voltage of the UK mains supply?

A

230 V

55
Q

How are most electrical appliances connected to the mains?

A

Using a cable

And a three pin plug

56
Q

What is the structure of an electrical cable?

A

Live wire - alternating voltage makes it dangerous

Neutral wire - earthed at the local substation

57
Q

What do oscilloscopes measure?

A

The peak potential difference and the frequency of a low voltage supply

58
Q

What is the brown wire connected to?

A

The live pin

59
Q

What is the blue wire connected to?

A

The neutral pin

60
Q

What is the green and yellow wire connected to?

A

The earth pin

61
Q

What does a three core cable contain?

A

Brown - live pin
Blue - neutral pin
Green and yellow - earth pin

62
Q

What does a two core able consist of?

A

Brown wire - live pin

Blue wire - neutral pin

63
Q

What happens if the current in a fuse wire exceeds the rating of the fuse?

A

It will melt

Breaking the circuit

64
Q

If an electrical fault causes too great a current, what happens?

A

The circuit is disconnected by a dude

Or w circuit breaker in the live wire

65
Q

Describe what materials are used for cables?

A

Copper - the wire because it is a good electrical conductor and easily bends

Covered in an outer layer of:
Rubber/plastic - good electrical insulator and so prevents anyone touching the cable recovering an electric shock

66
Q

When are two core cables used?

A

For appliances that have plastic cases

67
Q

What does the longest pin of a three pin plug do?

A

Makes contact with the Earth wire of a wall socket circuit
So when you plug an appliance with a metal case to a wall socket
The case is automatically earthed

68
Q

What are pins made of and why?

A

Brass
Because brass is a good conductor
And does not rust or oxidise

69
Q

Why aren’t pins made of copper?

A

Copper isn’t as hard as brass

70
Q

What is the case material of a plug?

A

An electrical insulator

The inside of the case is shaped so the wires and pins CAN NOT touch eachother when the plug is sealed

71
Q

How does a fuse work?

A

Is between the live pin and the live wire
If too much current passes through the wire in the fuse
It melts an cute the live wire off

72
Q

When are are thicker cables used?

A

When more current is needed
So wired need to be thicker
To stop th heating effect of the current making the wires too hot

73
Q

What is a fuse rating?

A

The maximum current that can pass through it without melting the fuse wire

74
Q

How is the fuse connected?

A

In series with the live wire between the live wire and the appliance

75
Q

What is a circuit breaker?

A

An electromagnetic switch that opens when there is a fault

76
Q

How does a circuit breaker work?

A

If the current in the live wire is too large
The magnetic field or th electromagnet is strong enough to pull the switch contacts apart
Which stops the current in the live wire flowing
And the switch stays open

77
Q

How is the electromagnet connected to the live wire?

A

In series

78
Q

Advantages of circuit breakers?

A

Work faster

Reset more quickly

79
Q

How does a residual current circuit breaker work?

A

A RCCB cute off the current in the live wore when it is different from the current in the neutral wire

80
Q

When can an RCCB be used?

A

When there is no earth connection

81
Q

Advantages of Residual current circuit breakers?

A

More sensitive than a fuse or an ordinary circuit breaker

Works even faster

82
Q

When would an appliance have no earth wire?

A

when it is double insulated

83
Q

When use a two core cable?

A

When the appliance is double insulated

And so no earth wire is needed

84
Q

When use a three core cable?

A

If an earth wire is needed because the appliance had a metal case

85
Q

How do you chose the thickness of a cable?

A

So the heating effect of the current in the cable is insignificant

86
Q

Advantages of LED?

A 
Used for spotlight
Operate at low voltage
And low power
There are much more efficient than filament bulbs
And last longer
87
Q

Disadvantage of filament bulbs?

A

Very inefficient

The energy from the hot bulb gradually makes the plastic party’s of the bulb socket brittle and they crack

88
Q

Why are electrical faults dangerous?

A

They can cause electric shocks and fires

89
Q

When use a two core cable?

A

When the appliance is double insulated

And so no earth wire is needed

90
Q

When use a three core cable?

A

If an earth wire is needed because the appliance had a metal case

91
Q

How do you chose the thickness of a cable?

A

So the heating effect of the current in the cable is insignificant

92
Q

What are low energy compact fluorescent bulbs used for?

A

Took lighting

93
Q

Advantages of LED?

A 
Used for spotlight
Operate at low voltage
And low power
There are much more efficient than filament bulbs
And last longer
94
Q

Disadvantage of filament bulbs?

A

Very inefficient

The energy from the hot bulb gradually makes the plastic party’s of the bulb socket brittle and they crack

95
Q

Why are electrical faults dangerous?

A

They can cause electric shocks and fires

96
Q

What is the current for an electrical appliance?

A

The charge that flows through every second

97
Q

What is the pd across any electrical appliance?

A

The energy transferred by each coulomb of charge that passes through it

98
Q

What is the power of any electrical appliance?

A

The energy transferred every second

99
Q

How does a resistor become hotter?

A

Electrons are made to pass through resistor by battery
Each electron collided with vibrating metal ions in resistor transferring energy to them
The ions therefore gain kinetic energy and vibrate more
The resistor becomes hotter

100
Q

When does an electrician use a two core able?

A

If the appliance is doubly insulated

No earth wire needed

101
Q

When does an electrician use a three core cable?

A

If an earth wire is needed because the appliance had a metal case

102
Q

How does an electrician select a cable for use?

A

Suitable thickness so the heating effect of the current in the cable is insufficient

103
Q

What materials does static electricity not work with?

A

Conductors

104
Q

What materials does static electricity work with?

A

Insulators

105
Q

What happens when a child moves down a plastic slide?

A

Electrons are transferred from the child to the plastic
DUE TO FRICTION
The child has a positive charge
The hairs on his head now all have a positive charge so repeal eachother

106
Q

What do you know if a child’s hair stands on end?

A

The charges have the same polarity

So they repeat

107
Q

What force causes static electricity?

A

Friction

108
Q

Why does static electricity not happen with a metal?

A

Charge would pass through

Metal is not an insulator (is a conductor)

109
Q

When would you fit a two core cable not a three core cable?

A

When it is double insulated

110
Q

How does an RCCB operate?

A

Detects a very small difference between the current in the live wire and neutral wire

111
Q

How does a diode work?

A

Large resistance in one way

Stops current flowing in the other way

112
Q

How does an RCCB workV

A

Detects difference in current between the live and neutral wire
Current flows to earth

113
Q

Definition of potential difference?

A

Energy transferred per coulomb of charge

114
Q

Difference between protostar and main sequence star?

A

Protostar is at a lower temperature
And dosent emit radiation
As nuclear fusion hasent started

115
Q

When does resistance happen?

A

Electrons passing through a torch bulb have to push their way through lots of vibrating ions in the metal filament
The ions resist the passage of electrons

116
Q

When does the resistance of a metal filament increase?

A

When the temperature increases
The ions in the metal filament vibrate more as temperature increases
They resist the passage of electrons

117
Q

What do oscilloscopes measure?

A

The peak potential difference and the frequency of low voltage ac supply p

118
Q

What happens when charge flows through a resistor?

A

Energy is transferred to the resistor which makes it get hotter

P2 - Physics (5 decks)

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