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2. Electricity Flashcards

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1
Q

What direction do electrons 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

Another phrase for energy transferred?

A

Work done

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14
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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15
Q

What is the power?

A

The rate at which energy is transformed

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16
Q

What charge do electrons have?

A

Negative

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17
Q

What direction do electrons flow in?

A

Opposite direction of the conventional current

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18
Q

What is charge?

A

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

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19
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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20
Q

What is current measured in?

A

Amps (A)

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21
Q

What is voltage?

A

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

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22
Q

What is voltage measured in?

A

Volts

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23
Q

What is electrical energy?

A

Energy carried by current and converted to heat and light energy

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24
Q

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

A

Yes

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25
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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26
Q

What is an electric current?

A

A movement of charge

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27
Q

What is electrolysis?

A

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

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28
Q

What happens when electrical current flows through a resistor?

A

Electrical energy is transformed into heat energy

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29
Q

Another phrase for energy transferred?

A

Work done

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30
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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31
Q

What is the power?

A

The rate at which energy is transformed

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32
Q

What charge do electrons have?

A

Negative

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33
Q

What is the unit for power?

A

Watt (W)

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34
Q

What happens to power as current increases?

A

Increases

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35
Q

What happens to a lamp when there is lower resistance?

A

the lamp is brighter

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36
Q

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

A

Push their way through vibrating electrons

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37
Q

What does the resistance in a circuit do?

A

Limit the current

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38
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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39
Q

What is the p.d. of cells?

A

The sum of the p.d. of each cell

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40
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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41
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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42
Q

Is the voltage across each branch in parallel the same?

A

Yes

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43
Q

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

A

Increases

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44
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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45
Q

An example of an ohmic conductor?

A

A wire

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46
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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47
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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48
Q

What component will make a forward bias?

A

Diode

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49
Q

What component will make a curve?

A

Filament lamp

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50
Q

What component will make a straight line?

A

A wire

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51
Q

What happens to resistance as light intensity increases?

A

It increases

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52
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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53
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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54
Q

What happens to materials that are oppositely charged?

A

They attract

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55
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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56
Q

What happens to materials that have the same charge?

A

They will repel each other

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57
Q

Are electrostatic forces contact or non-contact?

A

Non-contact forces that can act at a distance

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58
Q

What is an electric field?

A

The region where a charged object would experience a force

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59
Q

How is an electric field represented?

A

Using field lines

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60
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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61
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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62
Q

What is a uniform field?

A

A field for a force that has a constant size

63
Q

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

A

Field lines point outwards because like charges repel

64
Q

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

A

Field lines point inwards because unlike charges attract

65
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

66
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

67
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.

68
Q

Solutions for static electricity when refuelling?

A

Earth the fuel tank with a copper rod or connect the tanker to a place by a copper conductor

69
Q

How does paint spraying work?

A

Spray gun is charged and so are the paint particles, particles repel each other giving a fine spray. Object is charged opposite to paint so object attracts paint = even coat

70
Q

What is an electrostatic dust precipitator?

A

A mechanism that remove smoke, dust particles etc. from chimneys

71
Q

How do electrostatic dust precipitators work?

A

Dust particles gain charge as they pass through a grid

Dust particles are attracted to plates

Dust falls down the chimney when the particles are heavy enough or the plates are knocked

72
Q

What is direct current?

A

Current travels in one direction

73
Q

An example of direct current?

A

Simple circuit

74
Q

What is an alternating current?

A

Current repeatedly reversed its direction

75
Q

What measures the waves of an alternating current?

A

Oscilloscope

76
Q

What current do cells and batteries alway supply?

A

Direct current which always passes in the same direction

77
Q

What type of supply is mains electricity?

A

a.c. supply

78
Q

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

A

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

79
Q

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

A

50Hz

80
Q

What is a metal wire made up of?

A

A lattice of positive ions, surrounded by delocalised electrons

81
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

82
Q

What is drift velocity?

A

When a wire is connected to a battery, electrons have a random movement but move in the same direction through the wire with a steady but slow drift velocity

83
Q

What direction is electron flow?

A

Opposite to the direction of the conventional current

84
Q

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

A

Every 0.01 seconds

85
Q

Do electrons travel all the way from the cell to the appliance?

A

No

86
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

87
Q

Why is the casing of a plug made from plastic?

A

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

88
Q

What is the casing of a plug made from?

A

Plastic

89
Q

What do cables contain?

A

Copper wires

90
Q

Why do cables contain copper wires?

A

Because copper is a good conductor

91
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

92
Q

What are the pins in a plug made from?

A

Brass

93
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

94
Q

Where is the fuse in a plug?

A

Between the live pin and the live wire

95
Q

What does the fuse do?

A

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

96
Q

Which pin is the longest in a plug?

A

The earth pin

97
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

98
Q

What colour is the live wire?

A

Brown

99
Q

What does the live wire do?

A

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

100
Q

What colour is the neutral wire?

A

Blue

101
Q

What does a neutral wire do?

A

Completes the circuit

102
Q

What colour is the earth wire?

A

Yellow/green

103
Q

What does the earth wire do?

A

Prevents the appliance becoming ‘live’

104
Q

What type of cables are less likely to overheat?

A

Thick cables

105
Q

What will thin wires be used for?

A

Lighting

106
Q

What will thick wires be used for?

A

Electric cookers

107
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

108
Q

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

A

Current will be altered

109
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
110
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
111
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

112
Q

Describe the resistance and the current in a short circuit

A

No or very low resistance, very high current

113
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

114
Q

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

A

more components = more resistance

115
Q

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

A

more components = less resistance

116
Q

What unit do electrical companies bill customers in?

A

Kilowatt hours (kWh)

117
Q

What is 1 kWh?

A

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

118
Q

What is 1 kWh equal to in J?

A

3.6 million J

119
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

120
Q

What does a fuse contain?

A

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

121
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

122
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

123
Q

What size fuse are domestic appliances often fitted with?

A

3, 5 or 13A

124
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

125
Q

When are earth wires used?

A

If the appliance has a metal case

126
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

127
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

128
Q

What is the National Grid?

A

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

129
Q

What happens to heat loss as current increases?

A

It increases

130
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

131
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

132
Q

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

A

Transformers ‘step-down’ voltage to safer levels

133
Q

Advantages of overhead cables?

A

Cheap to install and repair

High, out of reach

134
Q

Advantages of underground cables?

A

Out of sight

Safe from weather conditions

135
Q

Disadvantages of overhead cables?

A

Unattractive

More likely to get damaged in storms

136
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

137
Q

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

A

20 kV

138
Q

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

A

400 kV

139
Q

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

A

230 V

140
Q

What is a thermistor affected by?

A

A change in temperature

141
Q

What is an LDR affected by?

A

A change in light intensity

142
Q

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

A

Use different temperatures of water

143
Q

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

A

Alter the distance between LDR and light source

144
Q

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

A

Resistance increases as temperature decreases

145
Q

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

A

Resistance increases as light intensity decreases

146
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

147
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

148
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

149
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

150
Q

What are thermistors and LDRs examples of?

A

Ohmic conductors

151
Q

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

A

They share applied voltage equally

152
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

153
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

154
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.

Physics (11 decks)

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