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
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
3
Q
what is convection?
A
heat transferred when a fluid warms up, becomes less dense and rises, transferring energy with it
4
Q
what is current?
A
the rate of flow of electric charge
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
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
7
Q
what is potential difference?
A
the energy transferred per unit charge
8
Q
what is power?
A
the energy transferred per second
9
Q
what is radiation (infra-red)?
A
the transfer of heat through infra-red radiation
10
Q
what is resistance?
A
a property of all materials that opposes the flow of electric current
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
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
13
Q
what is thermal conductivity?
A
a property of a material that measures the rate of energy transfer through a material
14
Q
what is energy transferred between?
A
energy stores
15
Q
what are the main energy stores?
A
- kinetic
- thermal
- chemical
- gravitational potential
- elastic potential
- electrostatic
- magnetic
- nuclear
16
Q
what are examples of objects with energy in kinetic energy stores?
A
anything moving has energy in its kinetic energy store
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
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
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)
20
Q
what are examples of objects with energy in elastic potential energy stores?
A
anything stretched, like springs and rubber bands
21
Q
what are examples of objects with energy in electrostatic energy stores?
A
e.g. two charges that attract or repel each other
22
Q
what are examples of objects with energy in magnetic energy stores?
A
e.g. two magnets that attract or repel each other
23
Q
what are examples of objects with energy in nuclear energy stores?
A
atomic nuclei release energy from this store in nuclear reactions
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)
25
how is energy transferred between stores mechanically?
an object moving due to a force acting on it, e.g. pushing, pulling, stretching or squashing
26
how is energy transferred between stores electrically?
a charge moving through a potential difference, e.g. charges moving around a circuit
27
how is energy transferred between stores by heating?
energy transferred from a hotter object to a colder object, e.g. heating a pan of water on a hob
28
how is energy transferred between stores by radiation?
energy transferred e.g. by light/sound waves, e.g. energy from the sun reaching earth by light
29
what is an example of a mechanical energy transfer?
driving a car
30
what is an example of an electrical energy transfer?
a phone
31
what is an example of a thermal energy transfer?
a radiator
32
what is an example of a radiative energy transfer?
process of photosynthesis
33
what is the law of conservation of energy?
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
34
what is a closed system?
a system that can be treated completely on it's own, without any matter being exchanged with the surroundings
35
what are some examples of energy transfers?
- a ball rolling up a slope
- a bat hitting a ball
- a car slowing down (without braking)
- an electric kettle boiling water
36
explain how a ball rolling up a slope is a transfer of energy
energy is transferred mechanically from the kinetic energy store of the ball to its gravitational potential energy store
37
explain how a bat hitting a ball is a transfer of energy
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
38
explain how a car slowing down (without braking) is a transfer of energy
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
39
explain how an electric kettle boiling water is a transfer of energy
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
40
what is an investigation for efficiency?
comparing the efficiency of different types of bouncy ball
41
what is the method for comparing the efficiency of different types of bouncy ball?
(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
42
what is the main source of error in the investigation into the efficiency of different types of bouncy ball?
measuring the final height
43
suggest improvements to the method of the investigation into the efficiency of different types of bouncy ball to overcome error
- 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
44
what do most energy transfers include?
some losses
45
what are losses from energy transfers often by?
heating
46
besides the law of conservation of energy, what is another important principle about energy?
energy is only useful when it is transferred from one store to a useful store
47
give an example of how input energy is often lost to thermal energy stores by heating
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)
48
the less energy wasted, the more ... a device is
efficient
49
how do we calculate efficiency?
efficiency = useful output energy transfer/input energy transfer
50
what is the wasted energy that's output by a device transferred to?
less useful stores
51
how is wasted energy that's output by a device transferred to less useful stores?
normally by heating, or by light and sound
52
as energy is transferred away from a device to its surroundings, what happens to the energy?
the energy often spreads out and becomes less concentrated; we say it dissipates
53
give an example of how energy is dissipated as it's transferred away from a device
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
according to the law of conservation of energy, what happens to the total amount of energy?
it stays the same
55
what are the three different ways that energy is transferred by heating?
1. conduction
2. convection
3. radiation
56
what happens when energy is transferred by heating?
- 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
what does conduction occur mainly in?
solids
58
why does conduction occur mainly in solids?
particles are held tightly together whereas particles in liquids and gases are further apart so conduction of energy is a lot slower
59
what describes how well an object transfers energy by conduction?
the thermal conductivity of an object
60
what is the thermal conductivity of metal like?
high
61
what is the thermal conductivity of liquids and gases like?
low
62
what does convection often occur in?
fluids (liquids and gases)
63
describe what convection currents are
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
what is an example of something we use that relies on convection to make warm air circulate around rooms?
radiators in buildings
65
how do you reduce convection?
you need to stop the fluid moving
66
what do clothes, blankets and foam cavity wall insulation all work by?
trapping pockets of air
67
how do clothes, blankets and foam cavity wall insulation all work by trapping pockets of air?
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
what can radiation travel through?
a vacuum
69
when energy is transferred by heating by radiation, what is the energy carried by?
infra-red waves
70
what do all objects continually do?
emit and absorb radiation
71
what do cooler objects do to the radiation emitted by hotter things, and what is the affect?
cooler objects will absorb the radiation emitted by hotter things, so their temperature increases
72
what type of surfaces are very good absorbers and emitters of radiation?
matt black
73
what type of surfaces are very poor absorbers and emitters of radiation?
light-coloured, smooth and shiny
74
what does insulating your house do?
reduces energy loss
75
what is an example of where energy in the home can be wasted?
windows
76
besides designing a house to lose less energy, what else can be done to save energy?
making things more efficient so they waste less energy
77
what is an example of making things more efficient so they waste less energy?
using energy-saving light bulbs instead of normal ones
78
what are some features of a house that can be designed to lose less energy?
- loft insulation
- hot water tank jacket
- double glazing
- thick curtains
- draught-proofing
- cavity walls and cavity wall insulation
79
how does loft insulation contribute to losing less energy?
fibreglass 'wool' laid on the loft floor and ceiling reduces energy loss from the house by conduction and convection
80
how does a hot water tank jacket contribute to losing less energy?
reduces conduction, keeping the water hot
81
how does double glazing contribute to losing less energy?
two layers of glass with an air gap between reduce conduction
82
how do thick curtains contribute to losing less energy?
reduce heat loss by convection and conduction through the windows
83
how does draught-proofing contribute to losing less energy?
strips of foam and plastic around doors and windows stop hot air going out - reducing convection
84
how do cavity walls and cavity wall insulation contribute to losing less energy?
- 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
what can energy lost from hot water pipes be reduced by?
- 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
how does the thickness of walls affect how quickly energy is transferred out of a building?
the thicker the walls, the lower the rate of energy transfer
87
besides the thickness of walls, what else affects their rate of energy transfer?
the thermal conductivity of the material the walls are made from
88
what does having a high thermal conductivity mean the rate of energy transfer will be like?
high
89
what does reducing friction do?
reduce energy loss
90
what does friction within a system lead to energy being lost by?
heating
91
how can friction be reduced?
- 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
when an object falls, what happens?
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
if something is thrown upwards by applying a force to it, what does the work done by the force cause?
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
what is energy transferred to/from an object's kinetic energy store equal to?
energy transferred from/to the object's gravitational potential energy store
95
what do elastic objects have?
elastic potential energy store
96
when an elastic object e.g. a spring is squashed by a moving object, what is done to the spring?
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
as a spring pushes an object back out after being squashed, what happens?
the spring transfers the energy back to the kinetic energy store of the object
98
when an elastic object is stretched or compressed, how can energy be lost?
some energy is transferred to the thermal energy store of the object, causing it to heat up
99
how do electrical circuits transfer energy?
electrically
100
when a device is plugged into a socket in the wall, what is it connected to?
the mains (i.e. the national grid)
- energy is transferred electrically from the mains to the device
101
what does a battery have energy in?
its chemical energy store
- this energy can be transferred electrically to devices in a circuit
102
what are some examples of electrical devices and how they transfer energy supplied?
- 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
how is some energy lost as it's transferred to devices?
energy is transferred to the thermal energy stores of the wires by heating
104
what are some examples of how some energy is lost in a device itself?
- 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
what do electrical appliances have?
power ratings
106
what is the amount of energy transferred to a device the same as?
the work done by the battery or mains when a current flows
107
what is power measured in?
watts (W)
108
what does the power rating of electrical appliances tell you?
how much energy is transferred to the appliance per second (the rate of energy transfer)
109
why are nuclear power stations often located by the coast?
a large volume of water is required for cooling
110
what does a high specific heat capacity tell us about a substance?
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
what is a practical for specific heat capacity?
comparing the specific heat capacities of salty and fresh water
112
what is the method for comparing the specific heat capacities of salty and fresh water?
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
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 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
why was it important to avoid boiling the water in the experiment for comparing the specific heat capacities of salty and fresh water?
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
what does the specific latent heat of fusion describe?
melting/freezing
116
what does the specific latent heat of vaporisation describe?
boiling/condensing
117
what is an investigation for thermal efficiency?
the affect of thickness of insulation on the rate of cooling
118
what is the method for an investigation on the affect of thickness of insulation on the rate of cooling?
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
