Electricity P1 Flashcards
(192 cards)
1
Q
Define energy
A
The ability to do work, energy allows matter to move or cause change and makes things happen
2
Q
Name 9 types of energy
A
Sound, kinetic, chemical, heat, light, elastic potential, gravitational potential, magnetic, nuclear
3
Q
Identify 4 ways to transfer energy
A
Mechanically (by a force doing work), electrically (work done by mpving charges), heating, radiation (light or sound)
4
Q
How do energy transfers work?
A
In order to increase an energy store, it must be transferred between stores. When a system (object or group of objects) changes energy is transferred into or away from the system between different types of energy stores
5
Q
What is the law of conservation of energy?
A
Energy can be transferred usefully, stored or dissipated but never created or destroyed
6
Q
Define work
A
To move an object with an applied force
7
Q
What must happen to move an object along a surface?
A
Frictional forces opposing the direction of motion must be overcome
8
Q
Define friction
A
An opposing force to direction of movement when two surfaces are in contact
9
Q
Equation for work
A
Work = force x distance
10
Q
What happens when an object is moved vertically?
A
Work is done against gravitational force and the objects gravitational potential increases
11
Q
What happens when an object is moved down?
A
It’s gravitational store decreases and the energy is equal to the work done by the force of gravity acting upon it
12
Q
Equation for weight/force
A
Weight= mass x gravitational field strength =force
13
Q
Equation for work done
A
Work done = Force x distance = weight x height
14
Q
Equation for change in gravitational potential energy
A
Change in gravitational potential energy = mass x gravitational field strength x change in height
15
Q
Three uses of mechanical springs
A
To provide a force, to provide flexibility, to absorb energy
16
Q
Equation for force of a spring
A
Force = spring constant(N/m) x extension (in metres)
17
Q
What happens when we stretch or compress a string?
A
They become deformed and we have had to put energy into doing this therefore the energy is now stored in the string in the form of elastic potential energy
18
Q
Equation for kinetic energy
A
0.5 x mass x velocity^2
19
Q
Define energy efficiency
A
Getting as much useful energy output as possible from a device
20
Q
Define being efficient
A
Performing in the best possible way with the least waste of time or effort
21
Q
What happens to waste energy?
A
It is dissipated to the surroundings which become warmer. It becomes increasingly spread out and less useful
22
Q
Compare CLF bulbs and filament bulbs
A
CLF bulbs transfer less energy as heat compared to filament bulbs therefore they require less power
23
Q
Equation for efficiency
A
Efficiency = useful energy out divided by total energy supplied in x 100
24
Q
Equation for energy, power and time
A
Energy = power x time
25
Define powering a device
To supply a device with mechanical or electrical energy
26
Define power
How quickly energy is used
27
Define thermal conductivity
The rate at which energy is transferred through a material
28
Define infrared radiation
A type of electromagnetic wave which transfers heat energy
29
Define a perfect black body
An object which absorbs all of the radiation which hits oyster and does not reflect/transmit any radiation
30
Name two factors affecting the specific heat capacity of a substance
Mass & type of substance
31
Equation for specific heat capacity
Change in energy required = mass x specific heat capacity x temperature change
32
Define specific heat capacity
The amount of energy needed to change the temperature of 1kg of a substance by 1 degree Celsius
33
Define u-value
Measures how effective a material is as an insulator, the lower it is the better the insulator
34
Name 6 ways of insulating your home
Loft insulation, cavity wall insulation, double glazing, draught proofing, carpets, radiators, have thick walls made from a material with a low thermal conductivity
35
Equation for payback time
Payback time = cost of installation divided by savings per year
36
Name 8 energy sources
Tidal, biomass, geothermal, nuclear, wind, hydroelectric, solar, fossil fuels
37
How does a fossil fuelled power plant work?
Burns coal, produces steam, turns the turbine, generates energy in the generator, energy is transformed in the transformer
38
How does hydroelectric power work?
Water is held behind a dam, rainwater is caught and runs through pipes and passes through a turbine, turbine is connected to generator to produce electricity
39
Name 6 advantages of hydroelectric power
Reliable except in times of drought, water can be stored until demand is high, no pollution, constant rate of electricity generation, lasts many decades, no fuel costs
40
Name 5 disadvantages of hydroelectric power
Expensive set up, people have to leave their homes, causes flooding of the valley (rotting vegetation releases methane and carbon dioxide), must operate for decades before profitable, habitats destroyed
41
How does geothermal energy work?
Several rocks contain radioactive substances which release heat energy whilst decaying, hot rocks can heat water which rises to the surface as steam which can be used to turn turbines connected to generators
42
Name 5 advantages of geothermal energy
Renewable, no fuel costs, no pollution, reliable, free resource
43
Name 4 disadvantages of geothermal power
Only possible in volcanic areas where hot rocks lie close to the surface, harmful gases released, most sites far from populations, high installation costs compared to amount of energy it produces
44
How does wind power work?
Wind farms set up in exposed areas like on moors and wind over the blades turns the turbine and therefore the generator inside it which produces electricity
45
Name 5 advantages of wind power
Wind is free, no pollution, used in remote locations, land under the turbine can still be used, no permanent damage to landscape
46
Name 5 disadvantages of wind power
Unreliable (only produce electricity 70-85% of time because they stop when the wind stops are is too strong), noisy, ugly, huge wind farms needed to supply a town or city with electricity (1500 turbines to replace one coal fired power station), initial costs are high
47
How does solar power work?
Generates electric currents directly from sunlight. Focusing sunlight generates heat to boil water and steam turns a turbine connected to a generator
48
Name 4 advantages of solar power
Once set up the energy is free, no pollution, used in remote locations, renewable
49
Name 4 disadvantages of solar power
Initial set up is expensive, only works during the day and when its sunny, require large amounts of land
50
How does wave energy work?
Lots of small wave powered turbines located around the coast, moving turbines are connected to a generator
51
Name 3 advantages of wave power
No pollution, minimal running costs, no fuel costs
52
Name 4 disadvantages of wave power
Cost up set up is high, disrupts sea life, unreliable since waves die out when wind drops, never likely to provide energy on a large scale
53
Name 4 advantages of fossil fuels
Produces a lot of energy, power plants always have fuel in stock to respond quickly to changes in demand, safer, cheaper running costs than some other energy resources
54
Name 6 disadvantages of fossil fuels
Non-renewable and running out, greenhouse gases released leading to global warming, sulphur dioxide released which causes acid rain, global dimming caused, high cost to set up power plants, coal mining makes a mess of the landscape
55
How does nuclear power work?
Originates from the splitting of uranium atoms which generates heat and produces steam to turn a turbine connected to a generator
56
Name 3 advantages of nuclear power
Reliable generation of electricity, no carbon dioxide or sulphur dioxide produced, meets basic deman
57
Name 3 disadvantages of nuclear power
Radioactive materials are dangerous, radioactive waste products need to be disposed of, expensive to decommission
58
Define electric current
Flow of electric charge (in coulombs). Current can only flow around a complete circuit if there's potential difference. Measured in amperes
59
What happens when charge builds up?
It spreads out and takes the route to the ground
60
Name the 2 types of circuit
Series and parallel
61
What do amps measure?
The amount of electric charge flowing each second
62
Equation for current
Current = charge divided by time (seconds)
63
How do electrons move through a circuit?
From the negative terminal of the battery to the positive terminal
64
When can a metal object hold charge?
When it is insulated from the ground
65
What happens when two negatively charged metal objects are brought into contact?
Electrons transfer from the negative to the positive object
66
Define resistance
How easy it is for current to get through a wire
67
What are resistors used for?
Slowing down the current
68
Name 5 factors affecting resistance
Thickness of wire, length of wire, material, temperature, whether components are in series or parallel
69
What is the relationship between thickness of wire and resistance?
The thicker the wire, the less resistance
70
What is the relationship between temperature and resistance?
Heating a wire increases its resistance
71
Define ohms law
The current through a conductor at constant temperature is directly proportional to the voltage across two points
72
Relationship between resistance, voltage and current
Resistance = voltage divided by current
73
Define an ohmic resistor
A wire in which the current and voltage are directly proportional
74
What is the relationship between length of wire and resistance?
The longer the wire, the higher the resistance
75
Is resistance higher in series or parallel and why?
Series because there are more pathways for current to flow in parallel
76
Define voltage
The amount of push in a circuit, the driving force of the circuit. Energy transferred per charge pressent
77
Describe current in a series circuit
Current is the same everywhere. The size of the current is determined by total potential difference of cells and total resistance of the circuit
78
Describe voltage in a series circuit
There is a higher voltage when there are more cells provided that they are connected the same way. The total potential difference of the supply is shared between components. Potential differences around a series circuit always add up to the source potential difference
79
Describe resistance in a series circuit
Total resistance of two components is the sum of their resistances because by adding a resistor in series the two resistors have to share the total potential difference. The pd and current through each resistor is lower and current is the same everywhere but is reduced when a resistor is added which means total resistance increases
80
Describe current in a parallel circuit
The current along the branches is equal to that flowing around the circuit
81
Describe voltage in a parallel circuit
Voltage is the same between components, full source voltage
82
Relationship between resistance and light intensity
The resistance of a light dependent resistor increases as the light intensity decreases
83
Define alternating current
Current that repeatedly changes direction, caused by the charge carriers moving one way and then the other, frequency defines how often direction changes
84
Define direct current
Current which flows in one direction only
85
How is alternating current produced and used?
Produced by generators and used in mains electricity that is distributed to our homes
86
Can alternating current be transferred efficiently over large distances?
Yes, with the help of transformers
87
How is direct current produced and used?
Produced by cells and batteries, created by a direct potential difference and use sod electronic circuits such as those in computers
88
Can direct current be transferred efficiently over large distances?
No
89
What would happen to an AC waveform on an oscilloscope screen if the time base is switched off?
A vertical line would appear
90
Give two reasons alternating currents are dangerous
Were used to electrocute animals, were used to electrocute people on the death penalty
91
Give three positives of alternating current
Half the price of direct, can be transmitted over great distances, efficient way to ‘step down’ voltage for common uses
92
Give three negatives of direct current
Expensive at $1million, no efficient way to ‘step down’ voltage for common uses, cannot be transmitted over great distances
93
Give one positive of direct current
Worked well for powering light bulbs
94
What does the live wire do?
Carries the alternating current from the supply at 230V
95
Colour of live wire
Brown
96
What does the neutral wire do?
Completes the circuit at 0V and carries away current
97
Colour of neutral wire
Blue
98
What does the earth wire do?
Stops the device becoming ‘live’, acts as a safety wire and protects the wiring, only carries current when there is a fault, it is also at 0V
99
Colour of earth wire
Green and yellow
100
Why are wires made of copper?
It is a good conductor which can be drawn out into long thin wires
101
Why are wires surrounded by plastic?
It is flexible and a good insulator
102
Why are the pins in a plug made of brass?
It is a good conductor
103
What happens if too much current passes through a fuse wire?
The fuse wire melts which cuts off the live wire
104
What is a nanowatt?
0.000000001W (8 zeros after decimal point)
105
What is a milliwatt?
0.001W (2 zeros after decimal point)
106
What is a kilowatt?
1000W
107
What is the equation for power, current and resistance?
Power = Current^2 x resistance
108
What is the equation for energy, coulomb, time?
Current = Coulomb divided by time
109
What is the equivalent in electrons to 1 coulomb?
6.2 x 10^18 electrons
110
What is the equation linking energy transferred, potential difference and charge?
Energy transferred = potential difference (V) x charge (Q)
111
Identify 5 ways energy gets from the power station to your home?
National grid, transformer, step down, step up, pylons
112
What is the national grid?
A system of cable and transformer connecting power stations to consumers. It transfers electrical power from any power station on the grid to any homes or industry etc on the grid
113
What are pylons?
Tall structures which carry electricity above the ground through aluminium cables
114
Give three advantages of overhead cables
Relatively cheap to link between tall towers, easy access to maintain, open to air cooling
115
Give three disadvantages of overhead cables
Ruin landscapes, vulnerable to weather, cut across large areas of land
116
Give four disadvantages of underground cables
Expensive, harder maintenance, hard to cool, need to mark where they are
117
What is the equation for primary and secondary voltage and number of turns?
Primary voltage divided by secondary voltage = primary number of turns divided by secondary number of turns
118
Why does the matte back metal case of a stove improve rate of energy transfer?
Black is a good emitter. Matte surfaces are better emitters than glossy surfaces
119
Give 2 environmental advantages of using a wood burning stove to heat a home rather than heaters which use electricity from fossil fuels
Fossil fuels release sulphur dioxide which causes acid rain, wood is a carbon neutral
120
How does a cavity wall reduce unwanted energy transfers?
The cavity wall insulation, the clock and the brick have a low thermal conductivities so less energy is transferred by conduction. The wall is thick because it has three layers
121
How are different energy stores changed by a boiler?
Chemical energy store of fuel decreases. Thermal energy store of the water increases. Thermal energy store of the air increases
122
What is the equivalent in joules to one megajoule?
1MJ = 1000000J
123
Equation for power, energy, time
Power = energy divided by time
124
Equation for power, current and resistance
Power = current^2 x resistance
125
Equation for charge, current and time
Charge = current x time
126
How do the readings change on an ammeter and voltmeter in a series circuit with a LDR and fixed resistor when environmental conditions change?
When light intensity increases, the resistance of an LDR decreases, overall resistance of the circuit decreases, potential difference across total resistance remains unchanged, current in ammeter increases, potential difference across fixed resistor increases and PD across LDR decreases, reading on the voltmeter decreases. Potential difference is shared between components in series, the lower the resistance of the LDR the smaller the share of the potential difference, trading on the voltmeter decreases
127
Identify 8 energy stores
Thermal, kinetic, elastic potential, gravitational potential, magnetic, electrostatic, nuclear, chemical
128
Give an example of water being transferred by heating
You could think of the kettle's heating element and the water as a two object system. Energy is transferred electrically to the thermal energy store of the kettle's heating element which transfers energy by heating to the water's thermal energy store
129
In what two ways can work be done?
When current flows work Is done against resistance in a circuit, when a force moves an object
130
What happens in terms of energy when a person throws a ball?
The initial force exerted by a person to throw a ball upwards does work, it causes an energy transfer from the chemical energy store of the person's arm to the kinetic energy store of the ball and arm
131
What happens in terms of energy when a car brakes?
The friction between a car's brakes and wheels does work as the car slows down which causes an energy transfer from the wheels' kinetic energy store to the thermal energy store of the surroundings
132
What happens in terms of energy in a collision between a car and a stationary object?
The normal contact force between the car and the object does work, it causes energy to be transferred from the car's kinetic energy store to other energy stores. Some energy may be transferred away by sound waves
133
How do falling objects transfer energy?
When something is dropped from a height it's accelerated by gravity, the gravitational force does work. As it falls energy from the object's gravitational potential energy store is transferred to its kinetic energy store. For a falling object when there's no air resistance energy lost from the GPE store is equal to energy gained in the kinetic energy store
134
What does air resistance do?
Acts against all falling objects, causes some energy to be transferred to other energy stores e.g thermal energy stores of the object and surroundings
135
How does energy in an object's kinetic energy store change?
Energy is transferred to this store when a moving object speeds up and is transferred away from this store when the object slows down
136
What does energy in the kinetic energy store depend on?
The greater its mass and the faster the object is travelling, the more energy in its kinetic energy store
137
What materials can store a lot of energy?
Materials that need to gain a lot of energy in their energy stores to warm up but also transfer loads of energy when they cool down again
138
How do you investigate specific heat capacity of a solid material? 10 points
Get a block of the substance with two holes in it (one for the heater and thermometer), measure mass of block, wrap in an insulating layer like thick layer of newspaper to reduce energy transferred to surroundings, measure initial temperature of the block, set potential difference of power supply to 10V, turn on power supply and start a stopwatch, when you turn on the power supply the current does work on the heater and transfers energy electrically from the power supply to the heaters thermal energy store, this energy is transferred to the materials thermal energy store by heating which causes temperature increase, measure temperature as block heats up using thermometer every minute and keep an eye on ammeter because the current should not change, after collecting 10 readings turn off the power supply
139
What 5 calculations do you need to do after heating up the block in order to work out its specific heat capacity?
Calculate power supplied to heater using potential difference x current, use this to calculate how much energy has been transferred to the heater by timesing power by time (seconds), plot graph of energy transferred to thermal energy store of block against temperature, find gradient of the straight part of the graph, to get specific heat capacity of the material do 1 divided by (gradient x mass of block)
140
What is a powerful machine?
One which transfers a lot of energy in a short space of time
141
What is conduction?
The process where vibrating particles transfer energy to neighbouring particles.
142
Describe what happens in conduction in 7 steps
Energy transferred to an object by heating is transferred to the thermal store of the object, this energy is shared across the kinetic energy store of the particles in the object, the particles in the part of the object vibrate more and collide with eachother , this causes energy to be transferred between particles' kinetic energy stores, this process continues throughout the object until energy is transferred to the other side of the object, then it is transferred to the thermal energy store of its surroundings
143
What is convection?
Energetic particles move away from hotter to cooler regions
144
Describe what happens in convection in 5 steps
Energy is transferred by heating to the thermal store of a liquid or gas, energy is shared across the kinetic energy stores of a gas or liquid's particles, when liquids or gases are heated particles move faster than in solids and the space between individual particles increases as the particles are able to move, this causes density of a region being heated to decrease, the warmer and less dense region rises above the denser cooler regions as liquids and gases flow so energetic particles move away from hotter to cooler regions
145
How can you reduce the friction between two objects' surfaces being rubbed together?
Use lubricants which are usually liquids like oil so can flow easily between objects and coat them
146
What do frictional forces do?
Cause some energy in a system to be dissipated
147
How does cavity wall insulation work?
Cavity walls are made up of an inner and outer wall with an air gap in the middle which reduces the amount of energy transferred by conduction through the walls. Cavity wall insulation fills the air gap with foam to reduce energy transfer by convection in the wall cavity
148
How does loft insulation work?
Can be laid out across the loft floor and ceiling, fibreglass wool is often used which is a good insulator as it has lots of pockets of trapped air. Loft insulation reduces energy loss by conduction and helps prevent convection currents from being created
149
What are convection currents?
A cycle where air particles are constantly being heated, rising, cooling then sinking
150
How do double glazed windows work?
Have an air gap between two sheets of windows to reduce energy transfer by conduction through windows
151
How do draught excluders work?
Put around doors and windows to reduce energy transfer by convection
152
How are electric heaters 100% efficient?
All the energy in the electrostatic energy store is transferred to useful thermal energy stores
153
Ultimately, where does all energy end up transferred to?
Thermal energy stores
154
Identify 2 ways transport uses non renewable energy resources
Petrol and diesel powered vehicles use fuel created from oil, coal is used in some old fashioned steam trains to boil water to produce steam
155
Identify a way transport uses renewable energy resources
Some vehicles run on pure biofuels
156
Identify 3 ways heating uses non renewable energy resources
Natural gas is used to heat water in homes which is pumped into radiators, coal is burnt in fireplaces, electric heaters use electricity generated from non renewables
157
Identify 3 ways heating uses renewable energy resources
Geothermal (or ground source) heat pumps use geothermal energy resources to heat buildings, solar water heaters use the sun to heat water which is then pumped into radiators in the building, burning bio fuel or using electricity from renewable resources can be used for heating
158
What is solar energy used to generate energy for?
Only used to generate energy on a small scale like to charge batteries in calculators and watches or to power road signs and satellites
159
How do tidal barrages work?
Tidal barrages are big dams that are built across river estuaries with turbines in them. As the tide comes in it fills up the estuary then water is allowed out through turbines at a controlled speed. Tides are produced by the gravitational pull of the sun and the moon
160
Identify 5 advantages of tidal barrages
Tides are pretty reliable (happen twice a day without fail and always near predicted height), no pollution, no fuel costs, minimal running costs, potential for generating a significant amount of energy
161
Identify 6 disadvantages of tidal barrages
Moderately high initial costs, alter habitat of wildlife, prevent free access by boats, spoil view, height of tide is variable so lower tides provide significantly less energy, don't work when water level is the same on either side of the barrage which happens four times a day
162
What are biofuels?
Renewable energy resources created from plant products or animal dung which can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same way as fossil fuels
163
Identify 2 pros of biofuels
Carbon neutral if the amount of CO2 released by burning is equal to the amount absorbed by plants you grow to make the biofuel, fairly reliable as crops take a relatively short time to grow
164
Identify 5 cons of biofuels
Cost to refine them so they are suitable for use is very high, growing crops specifically for biofuels will mean there isn't enough space or water to meet the demands for food, large areas of forest have been cleared to make room to grow biofuels which results in loss of species habitats, the decay and burning of this vegetation increases carbon dioxide and methane emissions, cannot meet immediate energy demands
165
How can acid rain be reduced?
Take sulphur out before burning fossil fuels
166
What 3 things has the UKs move towards renewable resources been triggered by?
Burning fossil fuels is very damaging to the environment, non renewables will run out one day so we need to learn to get by with renewables before this happens, , pressure from other countries caused the government to set targets for using renewables which puts pressure on energy providers to build renewable energy power plants so they don't lose business/money
167
Why is it difficult to change to renewable resources?
Scientists do not have the power to make companies/governments change their behaviour, building new renewable power plants costs money which some people don't want to pay for or can't afford to, arguments over where to put new power plants, some energy resources not as reliable as traditional fossil fuels, research on improving reliability and cost of renewables takes time and money, making personal changes like solar panels can be expensive
168
What is the size of current?
Rate of flow of charge
169
How does resistance of filament lamps change?
When an electrical charge flows through a filament lamp it transfers some energy to the thermal energy store of the filament which is designed to heat up. Resistance increases with temperature so as current increases the filament lamp heats up more and resistance increases
170
How does resistance of diodes change?
Resistance depends on direction of the current , they let current flow in one direction but have a very high resistance if the current is reversed
171
What does an ammeter do?
Measures current in camps flowing through the test wire in amps, must always be placed in series with whatever you're investigating
172
What does a voltmeter do?
Measure potential difference across the test wire in volts, must always be placed in parallel around whatever you're investigating
173
How can you investigate length of wire's effect on resistance? 6 steps
Attach crocodile clip to a test wire level with 0cm on a ruler, attach the second crocodile clip to the wire a certain distance from the first wire (e.g 10cm), close the switch on the circuit then record current through the wire and the pd across it, open switch then move crocodile clip another 10cm along wire, close the switch again and record new current and pd, keep repeating with different lengths then use your measurements of current and pd to calculate resistance for each length of wire
174
What is an I-V characteristic?
A graph which shows how current through a component changes as the pd across it is increased. Linear components like ohmic conductors' graphs are straight lines whereas non linear components like filament lamps have a curved line
175
How can you experiment to find a component's I-V characteristic? 5 steps
Set up a series circuit with a variable resistor, ammeter, battery and component with a voltmeter around it, vary the variable resistor to alter current flowing through the circuit and potential difference across the component, take several pairs of readings from ammeter and voltmeter to see how potential difference varies as current changes, repeat each reading 3 times to get an average pd at each current, swap over wires connected to the cell so direction of current is reversed
176
What is a light dependant resistor?
A resistor that is dependent on the intensity of light. In bright light resistance falls but in darkness resistance is very high. Used in automatic night light, outdoor lighting and burglar detectors
177
What is a thermistor?
A temperature dependant resistor. In hot conditions resistance drops and in cool conditions it increases so they make useful temperature detectors like electronic thermostats
178
What are sensing circuits used for?
Turning on or increasing the power to components depending on the conditions they are in
179
What is potential difference like in a sensing circuit with a thermistor and a fixed resistor with a fan around it?
Potential difference of the power supply is shared out between the thermistor and the loop made up of the fixed resistor and fan according to their resistances - the bigger a components resistance, the more of the potential difference it takes. As the heat of the room increases the thermistor's resistance falls so it takes less potential difference and the fan goes faster
180
What happens if you add a resistor into a parallel circuit?
The total resistance of two resistors is less than the resistance of the smallest of the two resistors. The current has more direction to flow in parallel to increases which means a decrease in current
181
How do you investigate the effect of placing resistors in a series circuit? 8 steps
Find at least 4 identical resistors, build a circuit with one resistor a battery and ammeter, make a note of pd of battery, measure current through circuit using an ammeter and calculate resistance, add another resistor in series with the first, measure current through circuit and work out resistance, repeat until you've used all resistors, plot a graph of number of resistors against total resistance of circuit
182
How do you investigate the effect of placing resistors in a parallel circuit? 8 steps
Find at least 4 identical resistors, build a circuit with one resistor a battery and ammeter, measure total current through circuit and calculate resistance using pd of the battery, add another resistor in parallel with the first, measure total current of circuit and calculate overall resistance of the circuit, repeat until you've used all resistors, plot a graph of number of resistors against total resistance of circuit
183
Why does touching a live wire give you an electric shock?
Your body like the earth is at 0V so touching the live wire produces a large potential difference across your body and a current flows through you
184
What happens if the link between the live wire and earth creates a low resistance path to earth?
A large current will flow which could result in a fire
185
What does total energy transferred depend on?
How long the appliance is on for and its power. Energy transferred = power x time
186
When is an appliance cheaper to run?
If they have a lower power rating because this means they use less energy in a given time
187
What happens when an electrical charge goes through a change in potential difference?
Energy is transferred, energy is supplied to the charge at the power source to 'raise' it through a potential. The charge gives up this energy when it falls through any potential drop in components elsewhere in the circuit.
188
Equation linking energy transferred, potential difference and charge flow
Energy transferred = Charge flow x potential difference. This means a battery with a bigger pd will supply more energy to the circuit for every coulomb of charge which flows round it because the charge is 'raised up' higher at the start
189
Equation linking potential difference, power and current
Power = potential difference x current
190
What does electricity production need to meet?
Electricity usage/demand which is highest when people get up in the morning or return from school/work. Power stations often run at well below their maximum power output so there's spare capacity to cope with a high demand even if there's an unexpected shut down of another site
191
What do you need in order to transmit huge amounts of energy?
Either a high potential difference or high current but the problem with high current is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings. It's much cheaper to boost the pd up really high and keep the current fairly low (the national grids does this). For a given power, increasing pd decreases current which decreases energy lost by heating wires etc
192
What does boosting the pd to 400,0000 to transmit power require?
Transformers as well as big pylons with huge insulators. Step up transformers step up potential difference at one end for efficient transmission then step down transformers bring it back down to safe usable levels at the other end
