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*AQA GCSE Physics* > 2. Electricity > Flashcards

2. Electricity Flashcards

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1
Q

What direction is ‘electron flow’ in?

A

Opposite direction of the conventional current

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2
Q

What is charge?

A

The electrons that are always in a wire - whether connected to a cell or not

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3
Q

What is current?

A

The flow of electrons in a conductor - when it’s connected to a cell in a complete circuit

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4
Q

What is current measured in?

A

Amps (A)

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5
Q

What is voltage?

A

The push and pull of electrons in a wire - makes electrons flow

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6
Q

What is voltage measured in?

A

Volts

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7
Q

What is electrical energy?

A

Energy carried by current and converted to heat and light energy

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8
Q

Is the current the same all the way round in series?

A

Yes

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9
Q

Why do electrical charges move through metals?

A

They have some electrons that are free to move from their atoms

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10
Q

What is an electric current?

A

A movement of charge

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11
Q

What is electrolysis?

A

When current flows in a liquid, carried by positive and negative ions

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12
Q

What happens when electrical current flows through a resistor?

A

Electrical energy is transformed into heat energy

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13
Q

What does the energy transferred depend on?

A

Amount of charge carried by electrons and p.d. Pushing the charge around

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14
Q

What charge do electrons have?

A

Negative

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15
Q

What is the unit for power?

A

Watt (W)

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16
Q

What happens to power as current increases?

A

Increases

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17
Q

What happens to a lamp when there is lower resistance?

A

the lamp is brighter

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18
Q

What do electrons have to do when passing through a wire?

A

Push their way through vibrating electrons

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19
Q

What does the resistance in a circuit do?

A

Limit the current

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20
Q

Ohms law?

A

The current through a resistor at a constant temperature is directly proportional to the potential difference across the resistor

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21
Q

What is the p.d. of cells?

A

The sum of the p.d. of each cell

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22
Q

In a series circuit…

A
  • the same current passes through the components
  • the p.d. of the voltage supply is shared between the components
  • the total resistance of components is equal to the sum of the resistance of each component
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23
Q

In a parallel circuit…

A
  • the total current through the whole circuit is the sum of the currents through the separate components
  • the p.d. across each branch is the same
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24
Q

Is the voltage across each branch in parallel the same?

A

Yes

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25
Q

What happens to current as resistance of a filament lamp increases?

A

Increases

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26
Q

What does a current - p.d. graph with a straight line show?

A

The resistance is constant, obeying Ohm’s law.

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27
Q

An example of an ohmic conductor?

A

A wire

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28
Q

What does a current - p.d. graph with a curve show?

A

The resistance isn’t constant, it increases as the temperature increases.

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29
Q

What does a current - p.d. graph with a forward/reverse bias show?

A

The resistance is not constant, it rapidly decreased and the current increases

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30
Q

What component will make a forward bias?

A

Diode

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31
Q

What component will make a curve?

A

Filament lamp

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32
Q

What component will make a straight line?

A

A wire

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33
Q

What happens to resistance as light intensity increases?

A

It increases

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34
Q

What is static electricity?

A

When charge builds up on an object and doesn’t move e.g. rubbing a rod

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35
Q

What will happen when two different rods are held close to each other?

A

They will attract if they have different charge

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36
Q

What happens to materials that are oppositely charged?

A

They attract

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37
Q

What will happen when two rods of the same material are held close to each other?

A

They will repel as they have the same charge

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38
Q

What happens to materials that have the same charge?

A

They will repel each other

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39
Q

Are electrostatic forces contact or non-contact?

A

Non-contact forces that can act at a distance

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40
Q

What is an electric field?

A

The region where a charged object would experience a force

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41
Q

How is an electric field represented?

A

Using field lines

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42
Q

What does the direction of a field line show?

A

The direction of the force that would act on a small positive charge at that point

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43
Q

What does the spacing of field lines show?

A

The strength of the force.

The closer together the lines, the stronger the force

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44
Q

What is a uniform field?

A

A field for a force that has a constant size

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45
Q

What direction do field lines point when an object is positively charged?

A

Field lines point outwards because like charges repel

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46
Q

What direction do field lines point when an object is negatively charged?

A

Field lines point inwards because unlike charges attract

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47
Q

What happens to field lines as you move away from the charged object?

A

Field lines spread out as you move away, so the force becomes weaker

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48
Q

How does a ‘Van de Graff’ generator work?

A

A charge builds up on the dome due to electrons being rubbed off by the belt. If charge is big enough then the voltage comes high enough to ionise the air molecules so electrons jump down to earth = electric current

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49
Q

Dangers with static electricity when refuelling?

A

Fuel gains electrons from pipe so pipe is positive and fuel negative. Resulting voltage may cause a spark.

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50
Q

What is direct current?

A

Current travels in one direction

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51
Q

An example of direct current?

A

Simple circuit

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52
Q

What is an alternating current?

A

Current repeatedly reversed its direction

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53
Q

What measures the waves of an alternating current?

A

Oscilloscope

54
Q

What current do cells and batteries alway supply?

A

Direct current which always passes in the same direction

55
Q

What type of supply is mains electricity?

A

a.c. supply

56
Q

What is the voltage of the live wire in an alternating current?

A

Alternates between +325V and -325V = 230V d.c.

57
Q

What is the frequency of the mains a.c. in the U.K.?

A

50Hz

58
Q

What is a metal wire made up of?

A

A lattice of positive ions, surrounded by delocalised electrons

59
Q

What happens to electrons when a wire is attached to the battery?

A

The free electrons are repelled by the negative terminal and attracted to the positive one

60
Q

What direction is electron flow?

A

Opposite to the direction of the conventional current

61
Q

How often do electrons change direction in an a.c. circuit?

A

Every 0.01 seconds

62
Q

How does a mains-powered appliance gets its energy if the electrons do not travel all the way from the power source?

A

The power sources causes all electrons in a circuit loop to vibrate at once; energy is transferred from electrons to appliance

63
Q

Why is the casing of a plug made from plastic?

A

Because it doesn’t conduct, it’s a good insulator

64
Q

What is the casing of a plug made from?

A

Plastic

65
Q

What do cables contain?

A

Copper wires

66
Q

Why do cables contain copper wires?

A

Because copper is a good conductor

67
Q

How is copper arranged in a wire?

A

The copper is made into lots of thin strands twisted together rather than one thick wire as this makes the cables more flexible

68
Q

What are the pins in a plug made from?

A

Brass

69
Q

Why are the pins in a cable made from brass?

A

It is a good conductor, it is stiff and does not corrode unlike copper

70
Q

Where is the fuse in a plug?

A

Between the live pin and the live wire

71
Q

What does the fuse do?

A

If current gets too high the fuse melts and breaks the circuit, cutting off the live wire

72
Q

Which pin is the longest in a plug?

A

The earth pin

73
Q

Why is the earth pin the longest in a plug?

A

To make contact with the earth wire of the socket, before contact with the live wire

74
Q

What colour is the live wire?

A

Brown

75
Q

What does the live wire do?

A

Alternates between +325V and -325V which is equivalent to a 230V d.c.

76
Q

What colour is the neutral wire?

A

Blue

77
Q

What does a neutral wire do?

A

Completes the circuit

78
Q

What colour is the earth wire?

A

Yellow/green

79
Q

What does the earth wire do?

A

Prevents the appliance becoming ‘live’

80
Q

What type of cables are less likely to overheat?

A

Thick cables

81
Q

What will thin wires be used for?

A

Lighting

82
Q

What will thick wires be used for?

A

Electric cookers

83
Q

What thickness of wire is used when?

A

Thin wires will be used for lower currents whereas thicker wires will be used for higher currents

84
Q

How is the amount of power for an object altered when connected to the mains electricity?

A

Current will be altered

85
Q

Describe a circuit when a wire has short-circuited one out of three bulbs

A
  • the resistance of the wire is almost zero
  • current flows through wire instead of lamp 1
  • current passes through two bulbs
  • loop is smaller and current is higher
  • bulbs are brighter
86
Q

Describe a circuit when a wire has short-circuited three bulbs

A
  • all 3 bulbs switch off
  • wire gets very hot
  • resistance of loops is zero
  • current is a lot higher
  • wire overheats
87
Q

What is a short circuit?

A

An electrical circuit that allows current to travel along unintended paths with no or very low resistance

Resistance low = current very high

88
Q

Describe the resistance and the current in a short circuit

A

No or very low resistance, very high current

89
Q

Why do lamps blow when they have just been turned on?

A

The lamp is cold so low resistance, high current flows - sometimes enough to melt the wire in the bulb

90
Q

What happens to resistance as you add components in a series circuit?

A

more components = more resistance

91
Q

What happens to resistance as you add components in a parallel circuit?

A

more components = less resistance

92
Q

What unit do electrical companies bill customers in?

A

Kilowatt hours (kWh)

93
Q

What is 1 kWh?

A

The energy delivered when a 1kW device is used for 1 hour

94
Q

What is 1 kWh equal to in J?

A

3.6 million J

95
Q

What does the cost of using a particular device depend on?

A

How fast it uses electrical energy (the power of the device) and how long it’s being used for

96
Q

What does a fuse contain?

A

A thin wire that heats up and melts if too much current passes through it

97
Q

What happens when a fuse ‘blows’?

A

The thin wire inside the fuse heats up and melts when too much current passes through it

98
Q

What happens if the current rating is too large?

A

The fuse will not blow when it should, and the heating effect could cause a fire in the appliance

99
Q

What size fuse are domestic appliances often fitted with?

A

3, 5 or 13A

100
Q

How do you work out which fuse to use for a particular appliance?

A

Need to know the power rating and working p.d. of the device so that you can calculate its working current

101
Q

When are earth wires used?

A

If the appliance has a metal case

102
Q

What happens when the live wire touches the case, in terms of the earth wire?

A

The large current surges down the earth wire and the fuse blows

103
Q

What happens if a fuse doesn’t blow because of incorrect rating?

A

The current will flow down the earth wire and the user won’t be electrocuted by touching the case

104
Q

What is the National Grid?

A

A network of transporters and power lines which ensure electricity is carried to where it is needed

105
Q

What happens to heat loss as current increases?

A

It increases

106
Q

What happens to voltage at the start of the national grid in power stations?

A

The voltage is ‘stepped-up’ (increased) using a transformer

107
Q

Why is voltage increased to transfer energy across the national grid?

A

Increasing the voltage reduces the current in the power lines which reduces energy in the cables, and heat energy produced

108
Q

What happens to voltage at the consumer end of the national grid?

A

Transformers ‘step-down’ voltage to safer levels

109
Q

Advantages of overhead cables?

A

Cheap to install and repair

High, out of reach

110
Q

Advantages of underground cables?

A

Out of sight

Safe from weather conditions

111
Q

Disadvantages of overhead cables?

A

Unattractive

More likely to get damaged in storms

112
Q

Disadvantages of underground cables?

A

Not as far from people e.g. digging roads

Expensive - digging tunnels

Difficult to know where they are when repairing

113
Q

What is the voltage from a power station before it is stepped up?

A

20 kV

114
Q

What is the voltage after it’s been stepped up?

A

400 kV

115
Q

What is the voltage after it’s been stepped down?

A

230 V

116
Q

What is a thermistor affected by?

A

A change in temperature

117
Q

What is an LDR affected by?

A

A change in light intensity

118
Q

Practically, how could you change the resistance of a thermistor?

A

Use different temperatures of water

119
Q

Practically, how could you change the resistance of a LDR?

A

Alter the distance between LDR and light source

120
Q

In a thermistor, what is the link between resistance and temperature?

A

Resistance increases as temperature decreases

121
Q

In a LDR, what is the link between resistance and light intensity?

A

Resistance increases as light intensity decreases

122
Q

What is the graph of a thermistor at a constant temperature? What does this mean for the resistance?

A

A straight line so its resistance is constant

123
Q

What is the graph of a LDR at a constant LI? What does this mean for the resistance?

A

A straight line so its resistance is constant

124
Q

What happens when temperature is increased in a circuit with a thermistor?

A

Resistance decreases. Current increased so a component may be turned on

125
Q

What happens when LI is increased in a circuit with a LDR?

A

Resistance decreases. Current increased so a component may be turn on

126
Q

What are thermistors and LDRs examples of?

A

Ohmic conductors

127
Q

In a potential divider, what happens to voltage when two resistors are equal?

A

They share applied voltage equally

128
Q

In a potential divider, a current passes through a resistor then through a thermistor. How is output voltage increased?

A

The thermistor cools. The resistance of the thermistor rises, taking a larger share of input voltage - so output voltage rises

129
Q

In a potential divider, a current passes through a thermistor then through a resistor. How is output voltage increased?

A

Temperature of the thermistor is increased and resistance decreases. The resistor takes a larger share of the input voltage - increasing the output

130
Q

In a potential divider, a current passes through a resistor then through a LDR. How is output voltage increased?

A

LI decreases, resistance increases, taking a larger share of the input voltage. So output voltage rises.

131
Q

What is power?

A

The rate at which energy is transformed

132
Q

Another phrase for energy transferred?

A

Work done

*AQA GCSE Physics* (10 decks)

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