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GCSE Edexcel Physics > Topic 2 - Conservation of Energy > Flashcards

Topic 2 - Conservation of Energy Flashcards

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1
Q

What is an energy store?

A

Where energy is stored, when energy is transferred to an object

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2
Q

Which objects have energy in a kinetic energy store?

A

Anything moving

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3
Q

Which objects have energy in a thermal energy store?

A

Any object. The hotter it is, the more energy it has in this store.

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4
Q

Which objects have energy in a chemical energy store?

A

Anything that releases energy by a chemical reaction, e.g., food, fuels

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5
Q

Which objects have energy in a gravitational potential energy store?

A

Anything that has a mass and is inside a gravitational field

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6
Q

Which objects have energy in a elastic potential energy store?

A

Anything that is stretched (or compressed), e.g., springs

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7
Q

Which objects have energy in a electrostatic energy store?

A

Anything with an electric charge which is interacting with another electric charge, e.g., two charges that attract or repel each other

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8
Q

Which objects have energy in a magnetic energy store?

A

Anything magnetic which is interacting with another magnet, e.g., two magnets that attract or repel each other

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9
Q

Which objects have energy in a nuclear energy store?

A

Atomic nuclei have energy in this store that can be released in nuclear reactions

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10
Q

What is a closed system?

A

An object that doesn’t let energy in or out of it. Energy can be transferred between different energy stores within the system, but no energy is transferred away from the system. This means that there is no net (overall) change in electricity in a closed system, so the total energy change is always zero.

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11
Q

What is an example of a closed system?

A

Soup inside a sealed thermos flask can be treated as a closed system. Energy cannot be transferred to or away from the soup, so it remains hot and the net change in the energy of the system is zero.

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12
Q

What are the four main ways that energy can be stored between stores?

A
  • Mechanically: an object moving due to a force acting on it, e.g. pushing, pulling, stretching or squashing.
  • Electrically: a charge (current) moving through a potential difference, e.g. charges moving round a circuit.
  • By heating: energy transferred from a hotter object to a colder object, e.g. heating a pan of water on a hob.
  • By radiation: energy transferred by waves, e.g. energy from the Sun reaching Earth by light.
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13
Q

What is work done?

A

Work done is just energy transferred. Work can be done electrically by a moving charge or mechanically by a force moving an object through a distance.

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14
Q

What are some examples of energy transfers involving work?

A
  • 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 arm and the ball. Energy is then transferred to the gravitational potential energy store of the ball.
  • A ball dropped from a height is accelerated by
    gravity. The gravitational force does work. It causes energy to be transferred mechanically from the ball’s gravitational potential energy store to its kinetic energy store (see page 68).
  • When a car slows down without braking, the friction between a car’s tyres and the road does work. Energy in the kinetic energy store of the car is transferred mechanically, and then by heating, to the thermal energy stores of the car and road.
  • 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 mechanically from the car’s kinetic energy store to other energy stores, e.g. the elastic potential and
    thermal energy stores of the object and the car body. Some energy will also be transferred away by sound waves
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15
Q

What is the conservation of energy principle?

A

Energy can be transferred usefully, stored, or dissipated, but can never be created or destroyed.

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16
Q

What happens to the energy when it is transferred between stores?

A

Not all of the energy is transferred usefully to the store that it is meant to go to. Some energy is always dissipated (wasted) when an energy transfer takes place. The useful energy has been transferred into thermal energy stores of the surroundings.

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17
Q

What is the equation for the conservation of energy principle?

A

total energy input = useful energy output + wasted energy

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18
Q

What is an example of conservation of energy?

A

A mobile phone is a system.
- When you use the phone, some energy is usefully transferred from the chemical energy store of the battery in the phone.
- Some energy is dissipated to the thermal energy store of the phone (when the phone feels warm)
- The total energy transferred from the chemical energy store of the phone’s battery is equal to the useful energy transferred to operate the phone, plus the energy dissipated to thermal energy stores.

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19
Q

What happens when work is done mechanically?

A
  • Some work has to be done against frictional forces
  • As work done is the same as energy transferred, which means that some energy must be transferred to overcome the frictional forces. This causes energy to be transferred to thermal energy stores (of the object doing the work and the surroundings)
  • They are being wasteful when they raise the temperature of the surroundings, because energy is being dissipated rather than transferred usefully
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20
Q

What is an energy transfer diagram?

A

Diagrams can make it easier to see what’s going on when energy is transferred. Boxes are used to represent energy stores, and arrows are used to show energy transfers.

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21
Q

What is a kinetic energy store?

A
  • Anything that is moving has energy in its kinetic energy store
  • Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down
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22
Q

What is the word formula for the energy in a kinetic store?

A

Kinetic energy = (1/2) * mass * (speed^2)

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23
Q

What is the symbol formula for the energy in a kinetic store?

A

KE = (1/2) * m * (v^2)

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24
Q

What are the units for kinetic energy?

A

J (joules)

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25
Q

What are the units for mass?

A

kg

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26
Q

What are the units for speed?

A

(m/s)^2

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27
Q

What does the formula for the energy in a kinetic store show?

A
  • Small mass, low speed - small amount of energy in kinetic energy store
  • Large mass, high speed - large amount of energy in kinetic energy store
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28
Q

What is a gravitational potential energy store?

A

There is a transfer of energy to the gravitational potential energy store of the raised object, as lifting an object in a gravitational field requires work. The higher an object is lifted, the more energy is transferred to this store.

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29
Q

What is the word formula for the energy in a gravitational potential energy store?

A

change in gravitational potential energy = mass * gravitational field strength * change in vertical height

30
Q

What is the symbol formula for the energy in a gravitational potential energy store?

A

ΔGPE = m * g * Δh

31
Q

What are the units for change in gravitational potential energy?

A

J (joules)

32
Q

What are the units for gravitational field strength?

A

N/kg

33
Q

What are the units for change in vertical height?

A

N/kg

34
Q

What is the gravitational field strength of the earth approximately?

A

10 N/kg

35
Q

What is the energy transfer for falling objects like?

A

When something falls, energy from its gravitational potential energy store is transferred to its kinetic energy store. The further it falls, the faster it goes. There is also no air resistance.

36
Q

What is the similarity between the energy lost from the GPE store and the energy gained in the kinetic energy store?

A

Energy lost from the GPE store = Energy gained in the kinetic energy store

37
Q

What is conduction?

A

Conduction is when one side of an object is heated, the particles in the hotter part vibrate more and collide with each other. This transfers energy from their kinetic energy stores to the kinetic energy stores of other particles, which then vibrate faster.It transfers energy through the object.

38
Q

What is thermal conductivity?

A

Describing how well a material transfers energy by conduction. For example, metals have a high thermal conductivity and gases (like air) have a low thermal conductivity.

39
Q

What happens if there is a low thermal conductivity?

A

In a building, the lower the thermal conductivity of its walls (the thicker the wall), the slower the rate of energy transfer through them, so it causes the building to cool slowly

40
Q

What do thermal insulators do?

A

Thermal insulators are objects made from materials that have a low thermal conductivity, that help reduce the amount of energy lost from a building

41
Q

What are cavity walls and what do they do?

A

Cavity walls are made up of an inner and an outer wall with an air gap in the middle, which reduces the amount of energy transferred by conduction through the walls, because air has a low thermal conductivity

42
Q

What is double glazing and what does it do?

A

Double-glazed windows have an air gap between two sheets of glass to prevent energy transfer by conduction through the windows

43
Q

What is loft insulation?

A

Fibreglass is an insulating material made of thin strands of glass that trap pockets of air. A thick layer of fibreglass wool laid out across the whole loft floor reduces conduction to the attic space, as the material (and the trapped air) are insulator

44
Q

What is a hot water tank jacket?

A

Putting fibreglass wool around a hot water tank reduces the energy transferred by conduction from the tank’s thermal energy store to the surroundings.

45
Q

What is lubrication?

A

For objects that are touching each other, lubricants can be used to reduce the friction between the objects’ surfaces when they move. Lubricants are usually liquids (like oil), so they can flow easily between objects and coat them.

46
Q

What are some examples of lubrication?

A
  • Cars need a good supply of engine oil to lubricate the moving parts in the engine and reduce the work done against friction. Without it, the engine will overheat as more work has to be done against friction, which causes more energy to be transferred to useless thermal energy stores.
  • Sewing machines have fast-moving parts which need to be lubricated with oil or grease to keep them working efficiently. When they are well lubricated, more of the energy supplied is transferred to the kinetic energy stores of the parts instead of being wasted to thermal energy
    stores.
47
Q

What is efficiency?

A

Efficiency compares the energy supplied to a device to the energy that is usefully transferred. The less energy that is ‘wasted’, the more efficient the device is.

48
Q

What is the equation to work out the efficiency?

A

efficiency = useful energy transferred by the device ÷ total energy supplied by the device

49
Q

Can a device be 100% efficient?

A

No device is 100% efficient and the wasted energy is usually transferred to useless thermal energy stores.

50
Q

What does efficiency on an energy transfer diagram show?

A
  • Wasted energy splits off vertically downwards
  • Useful energy continues straight
51
Q

How can you improve efficiency?

A
  • By lubrication and by thermal insulation
  • Decreasing the amount of wasted energy means that a higher proportion of the supplied energy is transferred to useful stores, so the efficiency of the process is increased
52
Q

What is an example of improving efficiency?

A

An electric fan usefully transfers energy electrically to the kinetic energy store of its blades, to cause the movement of air. It wastes energy in many ways, e.g. through friction between the axle and its supports. The efficiency could be improved by lubricating the axle.

53
Q

What are the non-renewable energy sources?

A
  • Coal
  • Oil
  • Natural gas
  • Nuclear fuels (e.g., uranium and plutonium)
54
Q

What are fossil fuels?

A

natural sources that form underground over millions of years, which are typically burnt to provide energy

55
Q

What are non-renewable fuels?

A

Fuels that do damage to the environment through emissions or because of issues with their mining, storage and disposal, but they do provide much of our energy

56
Q

What are the renewable energy sources?

A
  • Wind
  • Tides
  • Hydro-electricity
  • The sun (solar)
  • Bio-fuel
57
Q

What are renewable energy sources?

A
  • Energy sources that do damage to the environment
  • Don’t provide enough energy as non-renewable energy sources
  • Can be unreliable, as they depend on the weather
58
Q

What are energy sources used for?

A
  • Transport
  • Heating
  • Electricity used for transport and heating
59
Q

How are energy sources used in transport?

A
  • Petrol and diesel: fuel created from oil used to power many vehicles (including most cars).
  • Coal: used in some old-fashioned steam trains to boil water to produce
    steam.
60
Q

How are energy sources used in heating?

A
  • Natural gas: most widely used fuel for heating homes in the UK. The gas is burned to heat water, which is then pumped into radiators throughout the home.
  • Oil: some homes are heated by burning oil from a tank instead of gas, especially in remote places where it is difficult to connect to the gas supply.
  • Coal: commonly burnt in fireplaces.
61
Q

How are energy sources used in electricity used for transport and heating?

A

Renewable and non-renewable energy sources are used to generate electricity used for transport and heating

62
Q

What is wind power?

A

Wind power is created through the use of wind turbines. The blades turn with the wind, driving a generator, which produces electricity.

63
Q

What are solar cells?

A

Solar energy can be passive (e.g., positioning a building to gain heat from the sun, by placing near windows to the south-side of the building) or active (photovoltaic cells, which harness the sunlight energy and convert it to electricity)

64
Q

What are hydro-electric power stations?

A

Flooding a valley by building a dam. Water is allowed out at a controlled rate through turbines.

65
Q

What are tidal barrages?

A

A tidal barrage is a long dam that’s built across the mouth of the river, where it meets the sea. The barrage is constructed so that the incoming tide passes through turbines to generate electricity. It also harnesses the reverse flow of the water when the tide goes out.

66
Q

What are bio-fuels?

A

Bio-fuels are renewable energy sources - they’re created from either plant products or animal dung. They can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same way as fossil fuels

67
Q

What are the characteristics of fossil fuels?

A
  • provide a cost-effective energy source
  • reliable
68
Q

What are nuclear fuels?

A

nuclear fuels releasing energy to heat water into steam which drives the turbines

69
Q

How are fossil fuels being used more often?

A

Some of the UK’s electricity is produced from fossil fuels and nuclear power

70
Q

How are renewable energy sources being used more often?

A
  • Cars are electric
  • Government is thinking about managing without non-renewable energy sources and using renewable energy sources more often
71
Q

What are the factors affecting using more fossil fuels and renewable energy sources?

A
  • limited reliability
  • don’t know where to put new power plants
  • expensive

GCSE Edexcel Physics (15 decks)

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