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Physics Paper 1 > Topic 2 Electricity > Flashcards

Topic 2 Electricity Flashcards

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1
Q

What is current?

A

Flow of electrical charge

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2
Q

What must a closed circuit have in order for current to flow?

A

Source of potential difference

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3
Q

What 2 things does the current through a component depend on?

A
  • Potential difference across it
  • resistance of component
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4
Q

How does a greater resistance across a component affect the current (for a given potential difference)?

A

Current is smaller

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5
Q

What is the size of electrical current?

A

Rate of flow of charge

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6
Q

What is the equation to calculate charge flow?

A

Charge flow = current x time Q=IT

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7
Q

What are the units for charge flow?

A

Coulombs C

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8
Q

What is the value of the current in a single closed loop?

A

same at any point

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9
Q

What is potential difference?

A

Driving force that pushes charge round

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10
Q

What is resistance?

A

Anything that slows flow down

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11
Q

What are the units for resistance?

A

Ohms

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12
Q

What is the equation that links current, resistance and potential difference?

A

Potential difference = current x resistance V=IR

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13
Q

What does the resistance of an ohmic conductor do when the current changes?

A

Doesn’t change with the current (remains constant)

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14
Q

What are 2 examples of ohmic conductors?

A
  • Wire
  • Resistor
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15
Q

Through what component is the current (at a constant temperature) directly proportional to the potential difference across it?

A

Ohmic conductor

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16
Q

What are 4 components where the resistance does change with the current through them?

A
  • diode
  • filament lamp
  • thermistor
  • LDR
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17
Q

What does the resistance of a filament lamp increase with?

A

As temperature of filament increases

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18
Q

What happens when the current through a filament lamp increases?

A

Filament lamp heats up more and so resistance increases

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19
Q

What does the resistance depend on in a diode?

A

Direction of current

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20
Q

Where does the current through a diode flow?

A

In one direction only

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21
Q

When will a diode have a very high resistance?

A

If the flow of current is reversed

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22
Q

What is the resistance of an LDR dependent on?

A

Light intensity

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23
Q

What happens to the resistance of an LDR when light intensity increases?

A

Resistance decreases

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24
Q

What happens to the resistance of an LDR when light intensity decreases?

A

Resistance increases

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25
Q

What are 3 examples of applications of LDRs?

A
  • automatic night lights
  • outdoor lighting
  • burglar detectors
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26
Q

What is the resistance of a thermistor dependent on?

A

Temperature

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27
Q

What happens to the resistance of a thermistor when the temperature increases?

A

Resistance decreases

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28
Q

What happens to the resistance of a thermistor when the temperature decreases?

A

Resistance increases

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29
Q

What are 2 examples of applications of thermistors as temperature detectors?

A
  • electronic thermostats
  • car engine temperature sensors
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30
Q

What happens if you disconnect/remove one component in a series circuit?

A

Circuit is broken and all components stop

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31
Q

What is the rule for potential difference in series circuits?

A

Pd is shared between the components

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32
Q

What is the rule for current in series circuits?

A

Same current through each component

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33
Q

What is the size of the current in a series circuit determined by?

A

Total pd of cells and total resistance of circuit

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34
Q

What is the rule for resistance in a series circuit?

A

total resistance of two components is the sum of their resistances

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35
Q

In series circuits, why is the total resistance of two components, the sum of the resistance of each component?

A

By adding resistor in series, two resistors have to share total pd

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36
Q

What are the 2 types of electricity supply?

A
  • alternating current (ac)
  • direct current (dc)
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37
Q

What is alternating current produced by?

A

Alternating voltages

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38
Q

What is alternating current?

A

Current that regularly changes direction

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39
Q

What would alternating current appear as on a voltage-time graph?

A

curve alternating between positive and negative voltages

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40
Q

What type of supply is mains electricity?

A

ac (alternating current)

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41
Q

What voltage does the UK mains supply (electricity in the home) have?

A

230V

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42
Q

What is direct current?

A

Current that flows in only one direction

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43
Q

What is direct current produced by?

A

Direct voltage

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44
Q

What would direct current appear as on a voltage-time graph?

A

straight horizontal line at constant voltage

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45
Q

What type of current is supplied by cells and batteries?

A

Direct current

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46
Q

What is the frequency of the UK mains supply (electricity in the home)?

A

50Hz

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47
Q

What are most electrical appliances connected to the mains supply by?

A

three core cables

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48
Q

What does a three-core cable contain?

A

three wires, each with copper core and coloured plastic coating

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49
Q

How are the wires in a three-core cable made easily identifiable?

A

Insulation covering each wire is colour coded

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50
Q

What colour is the live wire?

A

Brown

51
Q

What colour is the neutral wire?

A

Blue

52
Q

What colour is the earth wire?

A

Green and yellow stripes

53
Q

What are the 3 wires inside a three-core cable called?

A
  • live wire
  • neutral wire
  • earth wire
54
Q

What does the live wire do?

A

Carries alternating pd from mains supply

55
Q

What does the neutral wire do?

A
  • completes circuit
  • when appliance operates normally, current flows through live and neutral wires
56
Q

What does the earth wire do?

A
  • safety wire
  • stops appliance from becoming live
57
Q

What is the voltage of the live wire?

A

230V (mains supply)

58
Q

What is the voltage of the neutral wire?

A

Close to 0V

59
Q

What is the voltage of the earth wire?

A

0V

60
Q

When is the only time the earth wire carries a current?

A

If there’s a fault

61
Q

What voltage is the body and earth at?

A

0V

62
Q

What happens if you touch a live wire?

A

large pd produced across your body and current flows through you (large electric shock)

63
Q

What is another way of saying a plug socket/light switch is turned off?

A

Switch is open

64
Q

Why is a live wire still dangerous even when the switch is open?

A

Current isn’t flowing but there’s still a pd in live wire

65
Q

When you make contact with a live wire, what is your body providing a link between?

A

Supply and the earth

66
Q

What does the earth wire provide?

A

Low resistance path to earth (instead of passing through a person)

67
Q

What are electrical appliances designed to do?

A

Transfer energy to components in circuit when current flows

68
Q

What 2 things does the amount of energy transferred by an appliance depend on?

A

How long appliance is switched on for and power of appliance

69
Q

When is work done/energy transferred in a circuit?

A

When charge flows

70
Q

What is the power of an appliance?

A

Energy it transfers per second

71
Q

What is the equation that links power, time and energy transferred?

A

Energy transferred = power x time

72
Q

What does a kettle transfer energy from?

A

Mains ac supply

73
Q

What does a kettle transfer energy to?

A

Thermal energy store of heating element inside kettle

74
Q

What does a handheld fan transfer energy from?

A

Battery

75
Q

What does a handheld fan transfer energy to?

A

Kinetic energy store of fans motor

76
Q

What is the equation that links power, potential difference and current?

A

Power = potential difference x current

77
Q

What is the equation that links power, current and resistance?

A

Power = (current)2 x resistance

78
Q

What is the equation that links energy transferred, charge flow and potential difference?

A

Energy transferred = charge flow x pd

79
Q

What are appliances labelled with that is their maximum operating power?

A

Power rating

80
Q

What does the power rating on an appliance tell you?

A

Maximum amount of energy transferred between stores per second when appliance is in use

81
Q

What does a lower power rating on an appliance tell you?

A

Uses less electricity in a given time- cheaper to run

82
Q

What is the National Grid?

A

System of cables and transformers linking power stations to consumers

83
Q

What does the National Grid do?

A

Transfers electrical power from power stations to consumers

84
Q

What do power stations often do so that there’s spare capacity to cope with high demand?

A

Run well below their maximum power output

85
Q

Why is the national grid an efficient way of transferring energy?

A

Uses high pd while keeping current low (decreases energy lost by heating wires and surroundings)

86
Q

What are used to increase the pd from power station to transmission cables in the national grid?

A

Step-up transformers

87
Q

What are used to decrease the pd (to a much lower value) for domestic use in the national grid?

A

Step-down transformers

88
Q

How do step-up transformers work?

A

Increases pd which decreases current- reducing power lost due to heating in cables

89
Q

What is static electricity?

A

When certain insulating materials are rubbed together, electrons are transferred, they become electrically charged

90
Q

What happens when certain insulating materials are rubbed together?

A

Negatively charged electrons are rubbed off one material and on to other

91
Q

What happens to the material that gains electrons (static electricity)?

A

Becomes negatively charged

92
Q

What happens to the material that loses electrons (static electricity)?

A

Left with equal positive charge

93
Q

What happens when 2 electrically charged objects are brought close together?

A

exert a force on each other

94
Q

What type of force is electrostatic attraction or repulsion?

A

Non-contact

95
Q

What can forces of attraction and repulsion cause objects to do?

A

Move

96
Q

What is a method to see objects exert forces of attraction or repulsion on each other?

A
  • suspend rod (with known charge) from piece of string (free to move)
  • placing object with same charge will repel rod (move away from object)
  • oppositely charged object - rod move towards object
97
Q

What happens when electric charge builds on an object?

A

Pd between object and earth increases

98
Q

How are sparks caused?

A

When pd between charged object and earth gets high enough

99
Q

What is an electric field created around?

A

Any electrically charged object

100
Q

Where is an electric field stronger?

A

Closer to charged object

101
Q

What happens to a charged object when placed in the electric field of another object?

A

experiences a force

102
Q

What does a high pd cause between a charged object and an earthed object?

A

Strong electric field

103
Q

How are sparks produced?

A

If electric field is strong enough, charges can be forced though insulators (air) and spark will occur

104
Q

How do we represent an electric field?

A

Using field lines

105
Q

In an electric field diagram, what do the arrows on field lines show?

A

What force would be on positive charge, if placed in field

106
Q

When the lines are closer together on an electric field diagram, is the field stronger or weaker?

A

Stronger

107
Q

When the lines are further apart and you get further from charge on an electric field diagram, is the field stronger or weaker?

A

Weaker

108
Q

What happens if you increase the distance between charged objects?

A

Strength of field decreases and force between them gets smaller

109
Q

What is the force between charged objects caused by?

A

Electric fields interacting

110
Q

What will the potential differences around a series circuit always add up to?

A

Total (source) pd

111
Q

How does adding resistors in series affect the total resistance?

A

Increases

112
Q

In a series circuit, if a component has a bigger resistance, is its share of the pd bigger or smaller?

A

Bigger

113
Q

Why does adding a resistor to a series circuit increase the total resistance (3 points)?

A

Pd across each resistor is lower
Current through each resistor is lower
Total current reduced as current same everywhere

114
Q

What happens to the cell pd if cells are connected in series?

A

Cell pd adds up, bigger pd

115
Q

What are ammeters always connected in?

A

Series

116
Q

What happens if you remove a component from a parallel circuit?

A

Hardly affect other components

117
Q

What is the rule for pd in parallel circuits?

A

Same across all components

118
Q

What is the rule for current in parallel circuits?

A

Total current = sum of currents through separate components (current shared between branches)

119
Q

In a parallel circuit, what does the total current going into a junction have to equal?

A

Total current leaving

120
Q

What is the rule for resistance in parallel circuits?

A

If 2 resistors in parallel, their total resistance is less than resistance of smallest resistor

121
Q

What does adding a resistor in parallel do to the total resistance?

A

Decreases

122
Q

Why does adding a resistor in parallel reduce the total resistance (3 points)?

A

Current has more routes- easier to flow
Increases total current

123
Q

What can dc series circuits be designed and used for?

A

Measure quantities and test components

Physics Paper 1 (4 decks)

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