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edexcel igcse physics > unit four: energy resources and energy transfer > Flashcards

unit four: energy resources and energy transfer Flashcards

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1
Q

stores of energy

A

food for chemical and then thermal energy
muscles transfer the chemical energy to movement energy
we need energy in the form of light and heating
some can be produced from the GPE of water in reservoirs and mountainous areas
geothermal energy
elastic potential energy in springs
main source is the sun

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2
Q

what energy stores are used in the production of electricity

A

chemical and nuclear

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3
Q

examples of wasted energy

A

energy can be transferred electrically to hot water in a tank (thermal energy store) in a house to be used when needed. although the tank may be well-insulated, some energy will be transferred from the water to other things like the metal tank and the surrounding air

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4
Q

principle of conservation of energy

A

energy is not created or destroyed in any process.

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5
Q

what happens when you exercise

A

the chemical energy stored in the body is transferred to movement energy. this could be transferred to e.g. a bicycle and could then be transferred as friction, and then to heat and sound.

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6
Q

how do we show how energy is transferred

A

sankey diagrams

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7
Q

efficency =

A

(useful energy output / total energy output) x 100%

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8
Q

what is thermal conduction

A

transfer of thermal energy through a substance by the vibration of the atoms within the substance.

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9
Q

what is a good thermal insualtor

A

wood

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10
Q

practical: investigate how well different metals conduct heat

A

have a steel rod and a copper rod with drawing pins stuck to them with petroleum jelly. heat the middle where they meet. the petroleum jelly will melt off and the copper drawing pins will fall, then the steel ones. to make it fair the rods must both be the saeme diamter and the drawing pins placed at equal points

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11
Q

what is convection

A

the transfer of thermal enegy through fluids but he upward movement of warmer, less dense regions of fluid.

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12
Q

practical: investigating convection currents

A

put potassium manganate in water

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13
Q

how does a convection current work

A

the water is heated just under the purple crystal which will colour the water as it dissolves. the heated water expands and becomes less dense than the colder surrounding water, so it floats to the top of the glass beaker. colder water sinks to take is place, and then is heated. the hot water at the top becomes more dense again and will begin to sink. a circulating current is formed.

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14
Q

how does a convector heater work

A

cold air drawn in at bottom, heating elements inside the vent and then warm air is pushed out of the top.

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15
Q

how does an oven work

A

heating element is placed at the bottom of the oven. it relies on convection.

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16
Q

what are convection currents responsible for

A

on shore and off shore breezes (land and sea breezes)

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17
Q

on shore breeze

A

the land heats up quicker

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18
Q

off shore breeze

A

the land cools down quicker than the sea

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19
Q

what is thermal radiation

A

the transfer of energy by infrared waves

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20
Q

what are heat waves called

A

IR waves or IR radiation

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21
Q

what is thermal imaging

A

thy can detect objects giving out IR radiation

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22
Q

what are good reflectors of thermal radiation

A

highly polished, shiny surfaces or white surfaces

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23
Q

practical: investigate how well different surfaces radiate heat

A

paint a filament bulb half black and then put two identical thermometers on either side of the bulb. the temperature that is facing the black side will rise faster than the other. the thermometers mus be fixed at the same height and distance from the bulb

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24
Q

if a surface is a good reflector of IR then it is

A

a poor radiatior of IR

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25
Q

what does the amount and type of energy radiated by a hot object depend on

A

surface texture, colour, and how hot it is

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26
Q

what does energy efficiency mean

A

using as much as possible of the energy we produce for the final purpose

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27
Q

how do the walls insualte a house

A

having an outer brick walland an inner wall made of thermal brick reduces heat loss by convection

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28
Q

how does the cavity or gap between the two walls help insulate a house

A

its wide enough for convection to circulate

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29
Q

what is the cavity or gap between the two walls filled with

A

glass fibre insulating wool is used to stop the convection currents in the air gap transferring thermal energy

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30
Q

outer brick wall is made of

A

bricks - good insulating properties, strong and will survive bad conditions

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31
Q

inner brick wall is made of

A

thermal bricks with good insulation properties. light, relatively cheap, and quick to work with.

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32
Q

how does double glazing work

A

two sheets of 6mm thick glass with an airtight seal of a low pressure gas and a spacer filled wth drying material to keep the gas between the glass panes dry

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33
Q

what happens if the glass is too thick or thin in double glazing

A

if too thin then insulation effect is reduced, and if too thick then convection currets can circulate.

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34
Q

how else can houses be kept warm

A

thermostats and computer control systems for central heating. these also reduce the house being heated too much by switching off when at the desired temperature.

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35
Q

how much energy is lost through the walls and windes

A

walls 35%

windows 10%

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36
Q

how do human clothes keep us warrm

A

hats reduce the large amount of body heat from the top of the head. clothes that trap air around the body dont allow air to circulate and keep us warm.

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37
Q

what does wind do that causes heat loss

A

forced convection

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38
Q

what does hypothermic mean

A

their body temp starts to fall

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39
Q

how do animals stay warm

A

birds fluff up their feathers (reducing heat loss from conduction)
penguins move closer together
some curl up in balls reducing the amount of their body exposed to the cold

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40
Q

energy def

A

the ability to do work

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41
Q

energy unit

A

joules

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42
Q 
work done (J) =
W =
A

force (N) x distance moved (m)

F x d

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43
Q

1 joule of work done is transferred

A

when a force of 1N is applied through a distance of 1m in the direction of the force

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44
Q

what is GPE

A

gravitational potential energy

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45
Q

when does an object have a lot of GPE

A

when its high off the ground

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46
Q

GPE (J) =

A

mass (kg) x g x height (m)

m x g x h

47
Q

KE (J) =

A

1/2 x mass (kg) x speed squared (m/s squared)

1/2 x m x vsquared

48
Q

power unit

A

watts

49
Q

power (watts) =

P =

A 
work done (J) / time taken (s)
W / t
50
Q

practical: investigate your power output

A

weight yourself to find your mass, (W newtons)
measure the height of one stair
calculate your GPE on various stairs

51
Q

density (kg/m cubed) =

ρ =

A

mass (kg) / volume (m cubed)

m / V

52
Q

practical: investigate the density of solids

A

use a half metre rule to measure the length, width and height of a regular solid. when measuring liquid vol displaced by an irregular object, make sure the measuring cylinder is on a level surface to avoid parallex error. then measure mass of solid. use weighing scales

53
Q

pressure (pascals) =

p

A

force (N) / area (sq m)

F / A

54
Q

in which direction does pressure in liquids and gases act

A

equally in all directions as long as the liquid is not moving

55
Q

what is the pressure exerted by the atmosphere on your body about

A

100 000 Pa

56
Q

mass of liquid =

A

(area x height) x density

(A x h) x ρ

57
Q 
pressure difference (Pa) = 
p =
A

height (m) x density (kg/m cubed) x g

h x ρ x g

58
Q

describe the structure and position of molecules in a solid substance

A

tightly packed
held in a fixed pattern or crystal substance by strong forces between them
vibrate around their fixed positions in the structure

59
Q

describe the structure and position of molecules in a liquid substance

A

tightly packed
are not held in fixed positions but are still bound together by strong forces between them
move at random with no fixed positions

60
Q

describe the structure and position of molecules in a gas substance

A

very spread out
no fixed positions and forces between them are very weak
move with rapid, random motion

61
Q

what is specific heat capacity

A

the amount of energy required to increase the temperature of 1 kilogram of a certain substance by 1 degree celsius.

62
Q

change in thermal energy (J) =

ΔQ

A

mass (kg) x specific heat capacity (c) x change in temperature (celsius)
m x c x ΔΘ

63
Q

practical: investigate the specific heat capacity of a substance

A

c = ΔQ / m x ΔΘ
measure the mass of the substance under test using electronic scales
measure intial temp and final temp using thermometer
determine amount of thermal energy supplied by using an electric immersion heater. (ΔQ = V x I x t)

64
Q

cause of gas pressure

A

when the molecules hit the walls of the container they exert a force. the combined effect of the huge number of collisions results in the pressure that is exerted on the walls of the container

65
Q

boyles law

A

when he doubled pressure, the volume of gas halved. p as proportional to 1/V

66
Q

p1V1 =

A

p2V2

67
Q

why can gases be compressed

A

because the gas molecules are very spread out

68
Q

if the gas is kept at the same temperature,

A

the average speed of the particles stays the same

69
Q

what is temperature an indication of

A

the average speed of the particles

70
Q

what did boyle make sure he did

A

conduct his experiment at a constant temperature because it has an effect on the pressure

71
Q

what is -273 degrees

A

absolute zero

72
Q

what does absolute zero mean

A

its the temperature where the pressure of a gas would be zero

73
Q

temperature in K =

A

temperature in C + 273

74
Q

temperature in C =

A

temperature in K - 273

75
Q

p1 / T1 =

A

p2 / T2

T must be in K

76
Q

Explain which colour is best at radiating thermal energy (2)

A

Black because it is a good emitter

77
Q

Explain how convection heats a room (4)

A

air next to radiator gains thermal energy
And spreads out, so the space between particles increases
This heated air is less dense
and therefore rises

78
Q

suggest how a rradiator an be designed to help maximise heat transfer by convection (1)

A

maximise surface area

increase temperature of hot water

79
Q

give the fossil fuels

A

coal, oil and natural gas

80
Q

how have fossil fuels been formed

A

in the ground by dead vegetation or tiny creatures by a process that has taken millions of years. once we have used them, it will take millions of years for new reserves of these fuels to be formed.

81
Q

how do fossil fuels harm the environment

A

by releasing greenhouse gases. these trap the suns heat in the earths atmosphere, causing global temp to rise.

82
Q

what does global warming cause

A

changes in the worlds climate and melting of polar ice caps

83
Q

order the fossil fuels in how much carbon dioxide they produce

A

coal, oil, natural gas

84
Q

what happens when you burn coal and oil containing sulfur

A

it is converted to sulfur dioxide, which is then released into the atmosphere where it combines with water to form acid rain.

85
Q

effects of acid rain

A

causes damage to people, plants and buildings.

86
Q

can you remove sulfur and sulfur dioxide

A

yes but both are very expensive

87
Q

what do nuclear reactors use to produce enrgy

A

uranium

88
Q

does nucler power produce greenhouse gases

A

no itss vlean

89
Q

adv of nuclear

A

no greenhouse or polluting gases

low cost per unit

90
Q

disadv of nuclear

A

stations are expensive to build
problem of disposal of nuclear waste
radioactive accidents

91
Q

how is electricity generated

A

water is heate.d this produces high pressure steam that makes the blades of a turbine spin. a turbine is like a windmill or a fan, but with many more blades. the turbine is used to turn the generator, which generates the electricity.

92
Q

wood as an energy resource

A

renewable
but produces pollution and greenhouse gases
wood valuable if not burnt because it can be used in building or making furniture

93
Q

how does HEP work

A

water wheels transfer the KE stored in rivers to break down corn and power industrial machinery. a water wheel (turbine) is used to turn the generators in a HEP station. these power stations use the GPE of water in high reservoirs in mountains. the GPE is transferred to KE as water flows down the mountain.

94
Q

how does tidal energy work

A

generate power by turning turbines as the tude flows into a blocked river estuary, as the tide falls and the water flows out of the estuary the turbines turn again

95
Q

how does wave energy work

A

the continous movement of the surface of the seas and oceans is the result of a combination of tides and wind.

96
Q

how does wind power work

A

wind turbine drive generators to provide electrical energy

97
Q

disadv of wind power

A

can only be harvested in windy regions. they cause environmental damage, noise pollution and kill birds and bats.

98
Q

what do photovoltaic cells do

A

transfer light energy directly to electrical energy

99
Q

what effiency are PV cells

A

15%

100
Q

adv of PV cells

A

provide a renewable energy resource that does not produce greenhoue gases

101
Q

disadv of PV cells

A

could spoil countryside. farming land could be lost

102
Q

solar panels absorb … and use it to….

A

thermal radiation to heat water

103
Q

how are solar panels placed in the northern hempishere

A

face south and be angled.

104
Q

how do solar panels work

A

water is pumped through copper pipes onto a copper sheet. copper is used because it is an excellent thermal conductor. the surfaces of the sheet and the pipes have a matte black finish for maximum absorption. the glass traps a layer of air above the copper to help insulate and retain heat. the backing is also designed to stop the escape of heat.

105
Q

how can electricity be used to generate solar heating

A

curved mirrors focus thermal radiation onto a boiler or pipes contianing water to produce steam. the mirrors are controlled to reflect the suns heat onto the central tower throughout the day

106
Q

how is geothermal energy produced

A

produced by the decay of radioactive elements like uranium.

107
Q

what is geothermal energy used for

A

domestic heating and hot springs.

108
Q

demand for energy

A

vaires all the time. (e.g. morning showers, tea in ad breaks etc)

109
Q

why can nuclear power stations not be turned on quickly

A

a fission reaction must start and and heating up the core takes time

110
Q

which is the quickest energy resource to turn on

A

HEP. they can also use extra electricity to pump water back into high level resevoirs.

111
Q

availability of power station

A

can be started moe quickly than nuclear but still take time. coal takes even longer. gas fired stations respond the quickest

112
Q

availibility of wind power

A

wind power dependent on strenth, direction and freq of wind. althoguh wind farms are loated in windy areas, they cannot be relied upon to produce electricity at times when it is needed most

113
Q

cost of nuclear

A

low maintance
high start up
high decomissioning
high disposal costs

114
Q

cost of wind

A

lower start up

pau back time very long

edexcel igcse physics (13 decks)

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