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physics > P7 - energy > Flashcards

P7 - energy Flashcards

1
Q

what is conduction?

A

the transfer of heat when particles gain kinetic energy and so vibrate more, colliding with particles next to them and therefore passing on the energy

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2
Q

what is conservation of energy?

A

the total amount of energy stored in a closed system is constant; it can only be transferred from one form to another

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3
Q

what is convection?

A

heat transferred when a fluid warms up, becomes less dense and rises, transferring energy with it

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4
Q

what is current?

A

the rate of flow of electric charge

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5
Q

what is efficiency?

A

a measure (usually a %) of how much energy is transformed into a useful form by a device or process

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6
Q

what is a kilowatt-hour?

A

a kilowatt-hour is the amount of energy transferred by a kilowatt device when switched on for 1 hour

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7
Q

what is potential difference?

A

the energy transferred per unit charge

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8
Q

what is power?

A

the energy transferred per second

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9
Q

what is radiation (infra-red)?

A

the transfer of heat through infra-red radiation

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10
Q

what is resistance?

A

a property of all materials that opposes the flow of electric current

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11
Q

what is specific heat capacity?

A

the specific heat capacity of a material is the amount of energy (J) needed to raise the temp of 1kg of that substance by 1 degree celsius

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12
Q

what is specific latent heat?

A

the energy needed to break intermolecular bonds and cause a change of state of 1kg of a material

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13
Q

what is thermal conductivity?

A

a property of a material that measures the rate of energy transfer through a material

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14
Q

what is energy transferred between?

A

energy stores

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15
Q

what are the main energy stores?

A
  • kinetic
  • thermal
  • chemical
  • gravitational potential
  • elastic potential
  • electrostatic
  • magnetic
  • nuclear
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16
Q

what are examples of objects with energy in kinetic energy stores?

A

anything moving has energy in its kinetic energy store

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17
Q

what are examples of objects with energy in thermal energy stores?

A

any object; the hotter it is, the more energy it has in this store

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18
Q

what are examples of objects with energy in chemical energy stores?

A

anything that can release energy by a chemical reaction, e.g. food, fuels

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19
Q

what are examples of objects with energy in gravitational potential energy stores?

A

anything in a gravitational field (i.e. anything which can fall)

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20
Q

what are examples of objects with energy in elastic potential energy stores?

A

anything stretched, like springs and rubber bands

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21
Q

what are examples of objects with energy in electrostatic energy stores?

A

e.g. two charges that attract or repel each other

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22
Q

what are examples of objects with energy in magnetic energy stores?

A

e.g. two magnets that attract or repel each other

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23
Q

what are examples of objects with energy in nuclear energy stores?

A

atomic nuclei release energy from this store in nuclear reactions

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24
Q

what are the four main ways that energy can be transferred between stores?

A
  • mechanical energy transfer
  • electrical energy transfer
  • thermal energy transfer (by heating)
  • radiative energy transfer (by radiation)
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25
Q

how is energy transferred between stores mechanically?

A

an object moving due to a force acting on it, e.g. pushing, pulling, stretching or squashing

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26
Q

how is energy transferred between stores electrically?

A

a charge moving through a potential difference, e.g. charges moving around a circuit

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27
Q

how is energy transferred between stores by heating?

A

energy transferred from a hotter object to a colder object, e.g. heating a pan of water on a hob

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28
Q

how is energy transferred between stores by radiation?

A

energy transferred e.g. by light/sound waves, e.g. energy from the sun reaching earth by light

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29
Q

what is an example of a mechanical energy transfer?

A

driving a car

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30
Q

what is an example of an electrical energy transfer?

A

a phone

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31
Q

what is an example of a thermal energy transfer?

A

a radiator

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32
Q

what is an example of a radiative energy transfer?

A

process of photosynthesis

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33
Q

what is the law of conservation of energy?

A

energy can be stored, transferred between stores, and dissipated - but can never be created or destroyed; the total energy of a closed system has no net change

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34
Q

what is a closed system?

A

a system that can be treated completely on it’s own, without any matter being exchanged with the surroundings

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35
Q

what are some examples of energy transfers?

A
  • a ball rolling up a slope
  • a bat hitting a ball
  • a car slowing down (without braking)
  • an electric kettle boiling water
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36
Q

explain how a ball rolling up a slope is a transfer of energy

A

energy is transferred mechanically from the kinetic energy store of the ball to its gravitational potential energy store

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37
Q

explain how a bat hitting a ball is a transfer of energy

A

some energy in the kinetic energy store of the bat is transferred mechanically to the thermal energy stores of the bat, the ball and their surroundings; some energy is transferred mechanically from the kinetic energy store of the bat to the kinetic energy store of the ball; the rest of the energy is carried away by sound

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38
Q

explain how a car slowing down (without braking) is a transfer of energy

A

energy in the kinetic energy store of the car is transferred mechanically (due to friction between the tyres and road) and then by heating to the thermal energy stores of the car and road

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39
Q

explain how an electric kettle boiling water is a transfer of energy

A

energy is transferred electrically from the mains to the thermal energy store of the kettle’s heating element; it is then transferred by heating to the thermal energy store of the water

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40
Q

what is an investigation for efficiency?

A

comparing the efficiency of different types of bouncy ball

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41
Q

what is the method for comparing the efficiency of different types of bouncy ball?

A

(use different balls for different experiments/compare results)
1. calculate the GPE of the ball from where you’re dropping it; mass x g x height; measure mass using a balance and height using a metre ruler
2. drop the ball and then catch it at it’s maximum height when it bounces back
3. calculate the GPE using this height and compare to original to find efficiency; ((useful output/total input)x100)
4. carry out repeats to calculate a mean

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42
Q

what is the main source of error in the investigation into the efficiency of different types of bouncy ball?

A

measuring the final height

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43
Q

suggest improvements to the method of the investigation into the efficiency of different types of bouncy ball to overcome error

A
  • we could record it and play back in slow motion in order to pause it to see height
  • get down to head height as this reduces parallax error
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44
Q

what do most energy transfers include?

A

some losses

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45
Q

what are losses from energy transfers often by?

A

heating

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46
Q

besides the law of conservation of energy, what is another important principle about energy?

A

energy is only useful when it is transferred from one store to a useful store

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47
Q

give an example of how input energy is often lost to thermal energy stores by heating

A

a motor will transfer energy to its kinetic energy store (useful) but will also transfer energy to the thermal energy stores of the motor and the surroundings (wasted)

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48
Q

the less energy wasted, the more … a device is

A

efficient

49
Q

how do we calculate efficiency?

A

efficiency = useful output energy transfer/input energy transfer

50
Q

what is the wasted energy that’s output by a device transferred to?

A

less useful stores

51
Q

how is wasted energy that’s output by a device transferred to less useful stores?

A

normally by heating, or by light and sound

52
Q

as energy is transferred away from a device to its surroundings, what happens to the energy?

A

the energy often spreads out and becomes less concentrated; we say it dissipates

53
Q

give an example of how energy is dissipated as it’s transferred away from a device

A

a pan of water on a hob; the hob will transfer energy to the water, but some energy will be dissipated to the surrounding air by heating

54
Q

according to the law of conservation of energy, what happens to the total amount of energy?

A

it stays the same

55
Q

what are the three different ways that energy is transferred by heating?

A
  1. conduction
  2. convection
  3. radiation
56
Q

what happens when energy is transferred by heating?

A
  • when an object is heated, energy is transferred to its thermal energy store and its temperature increases
  • the energy transferred is equal to m x specific heat capacity x temperature change
  • if energy is transferred by heating from a hotter object to a cooler object, the hotter object’s temperature will decrease and the cooler object’s temperature will increase
57
Q

what does conduction occur mainly in?

A

solids

58
Q

why does conduction occur mainly in solids?

A

particles are held tightly together whereas particles in liquids and gases are further apart so conduction of energy is a lot slower

59
Q

what describes how well an object transfers energy by conduction?

A

the thermal conductivity of an object

60
Q

what is the thermal conductivity of metal like?

A

high

61
Q

what is the thermal conductivity of liquids and gases like?

A

low

62
Q

what does convection often occur in?

A

fluids (liquids and gases)

63
Q

describe what convection currents are

A

as the warmer fluid rises, cooler fluid takes it’s place; the process continues until you end up with a circulation of fluid (convection currents)

64
Q

what is an example of something we use that relies on convection to make warm air circulate around rooms?

A

radiators in buildings

65
Q

how do you reduce convection?

A

you need to stop the fluid moving

66
Q

what do clothes, blankets and foam cavity wall insulation all work by?

A

trapping pockets of air

67
Q

how do clothes, blankets and foam cavity wall insulation all work by trapping pockets of air?

A

the air can’t move so the energy has to conduct very slowly through the pockets of air, as well as the material in between

68
Q

what can radiation travel through?

A

a vacuum

69
Q

when energy is transferred by heating by radiation, what is the energy carried by?

A

infra-red waves

70
Q

what do all objects continually do?

A

emit and absorb radiation

71
Q

what do cooler objects do to the radiation emitted by hotter things, and what is the affect?

A

cooler objects will absorb the radiation emitted by hotter things, so their temperature increases

72
Q

what type of surfaces are very good absorbers and emitters of radiation?

A

matt black

73
Q

what type of surfaces are very poor absorbers and emitters of radiation?

A

light-coloured, smooth and shiny

74
Q

what does insulating your house do?

A

reduces energy loss

75
Q

what is an example of where energy in the home can be wasted?

A

windows

76
Q

besides designing a house to lose less energy, what else can be done to save energy?

A

making things more efficient so they waste less energy

77
Q

what is an example of making things more efficient so they waste less energy?

A

using energy-saving light bulbs instead of normal ones

78
Q

what are some features of a house that can be designed to lose less energy?

A
  • loft insulation
  • hot water tank jacket
  • double glazing
  • thick curtains
  • draught-proofing
  • cavity walls and cavity wall insulation
79
Q

how does loft insulation contribute to losing less energy?

A

fibreglass ‘wool’ laid on the loft floor and ceiling reduces energy loss from the house by conduction and convection

80
Q

how does a hot water tank jacket contribute to losing less energy?

A

reduces conduction, keeping the water hot

81
Q

how does double glazing contribute to losing less energy?

A

two layers of glass with an air gap between reduce conduction

82
Q

how do thick curtains contribute to losing less energy?

A

reduce heat loss by convection and conduction through the windows

83
Q

how does draught-proofing contribute to losing less energy?

A

strips of foam and plastic around doors and windows stop hot air going out - reducing convection

84
Q

how do cavity walls and cavity wall insulation contribute to losing less energy?

A
  • two layers of brick with a gap between them reduce conduction but energy is also transferred across the gap by convection
  • squirting insulating foam into the gap traps pockets of air to minimise this convection
85
Q

what can energy lost from hot water pipes be reduced by?

A
  • covering pipes with insulation to reduce conduction and convection
  • painting the pipes white to reduce energy loss by radiation
  • making pipes as short as possible, so water spends less time in pipes
  • making pipes as wide as possible to reduce SA:V, this means smaller fraction of water in pipes is next to surface of pipe so less energy lost by conduction
86
Q

how does the thickness of walls affect how quickly energy is transferred out of a building?

A

the thicker the walls, the lower the rate of energy transfer

87
Q

besides the thickness of walls, what else affects their rate of energy transfer?

A

the thermal conductivity of the material the walls are made from

88
Q

what does having a high thermal conductivity mean the rate of energy transfer will be like?

A

high

89
Q

what does reducing friction do?

A

reduce energy loss

90
Q

what does friction within a system lead to energy being lost by?

A

heating

91
Q

how can friction be reduced?

A
  • lubrication e.g. using oil on a bike chain
  • changing shape of the object e.g. making a car more streamlined (reduces friction from air resistance)
92
Q

when an object falls, what happens?

A

work is done on the object by the force due to gravity; some of the energy in its gravitational potential energy store is transferred to its kinetic energy store

93
Q

if something is thrown upwards by applying a force to it, what does the work done by the force cause?

A

the work done by the force causes it to gain height; and energy in its kinetic energy store is transferred to its gravitational potential energy store

94
Q

what is energy transferred to/from an object’s kinetic energy store equal to?

A

energy transferred from/to the object’s gravitational potential energy store

95
Q

what do elastic objects have?

A

elastic potential energy store

96
Q

when an elastic object e.g. a spring is squashed by a moving object, what is done to the spring?

A

work is done on the spring and energy is transferred from the object’s kinetic energy store to the spring’s elastic potential energy store

97
Q

as a spring pushes an object back out after being squashed, what happens?

A

the spring transfers the energy back to the kinetic energy store of the object

98
Q

when an elastic object is stretched or compressed, how can energy be lost?

A

some energy is transferred to the thermal energy store of the object, causing it to heat up

99
Q

how do electrical circuits transfer energy?

A

electrically

100
Q

when a device is plugged into a socket in the wall, what is it connected to?

A

the mains (i.e. the national grid)
- energy is transferred electrically from the mains to the device

101
Q

what does a battery have energy in?

A

its chemical energy store
- this energy can be transferred electrically to devices in a circuit

102
Q

what are some examples of electrical devices and how they transfer energy supplied?

A
  • energy is transferred to the kinetic energy store of a motor
  • energy is transferred to the thermal energy store of a kettle’s heating element
  • energy is carried away from a speaker by sound waves
  • energy is carried away from a bulb by light waves
103
Q

how is some energy lost as it’s transferred to devices?

A

energy is transferred to the thermal energy stores of the wires by heating

104
Q

what are some examples of how some energy is lost in a device itself?

A
  • a motor heats up as energy is transferred to its thermal energy store due to friction
  • a heating element within a kettle will also transfer energy to the thermal energy stores of the kettle and the surroundings
105
Q

what do electrical appliances have?

A

power ratings

106
Q

what is the amount of energy transferred to a device the same as?

A

the work done by the battery or mains when a current flows

107
Q

what is power measured in?

A

watts (W)

108
Q

what does the power rating of electrical appliances tell you?

A

how much energy is transferred to the appliance per second (the rate of energy transfer)

109
Q

why are nuclear power stations often located by the coast?

A

a large volume of water is required for cooling

110
Q

what does a high specific heat capacity tell us about a substance?

A

the higher the specific heat capacity, the more energy the material can hold and the longer it will take to heat up or cool down

111
Q

what is a practical for specific heat capacity?

A

comparing the specific heat capacities of salty and fresh water

112
Q

what is the method for comparing the specific heat capacities of salty and fresh water?

A
  1. weight the beaker on the balance before and after it has water in, to work out the water’s mass
  2. set up the circuit and record starting temperature of water with thermometer (beaker has immersion heater in)
  3. start the stopcock when you turn the current on and keep doing the experiments for a set amount of time e.g. 7 minutes
  4. record the current and p.d. from the ammeter and voltmeter
  5. when you stop the stopclock, record the finishing temperature of water with thermometer and calculate temperature change
  6. work out energy using current, p.d. and time
  7. work out specific heat capacity using mass, energy and temperature change
113
Q

what is wrong with the experiment for comparing the specific heat capacities of salty and fresh water and what could be done to improve?

A
  • a lot of energy supplied by the heater went into the thermal store of the surroundings; to improve, ensure the heater is fully submerged and insulate the beaker/use a lid
  • some energy was used to heat the heater; to improve, wait long enough for the heater to dissipate its heat into the water at the end of the experiment
114
Q

why was it important to avoid boiling the water in the experiment for comparing the specific heat capacities of salty and fresh water?

A

energy would have been used to overcome intermolecular bonds rather than raise the temperature of the water and we wouldn’t have accounted for this in our calculation

115
Q

what does the specific latent heat of fusion describe?

A

melting/freezing

116
Q

what does the specific latent heat of vaporisation describe?

A

boiling/condensing

117
Q

what is an investigation for thermal efficiency?

A

the affect of thickness of insulation on the rate of cooling

118
Q

what is the method for an investigation on the affect of thickness of insulation on the rate of cooling?

A
  1. wrap the 5 boiling tubes in insulation (none/1 layer/2 layers etc)
  2. fill up 5 boiling tubes with boiling water and record the starting temperatures of each, they all need to start from the same temperature e.g. 70 degrees celsius
  3. begin the stopclock and put cotton wool on the top of the tubes so that heat can’t escape from the top
  4. after 5 minutes, record the finishing temperatures of each boiling tube and then you can calculate temperature changes
  5. for accuracy, carry out repeats of the experiment and then calculate a mean (remembering to exclude any anomalies from this calculation)
  6. plot the results onto a graph in order to visually represent the conclusion of the experiment
119
Q
A

physics (11 decks)

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