unit four: energy resources and energy transfer Flashcards
stores of energy
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
what energy stores are used in the production of electricity
chemical and nuclear
examples of wasted energy
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
principle of conservation of energy
energy is not created or destroyed in any process.
what happens when you exercise
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.
how do we show how energy is transferred
sankey diagrams
efficency =
(useful energy output / total energy output) x 100%
what is thermal conduction
transfer of thermal energy through a substance by the vibration of the atoms within the substance.
what is a good thermal insualtor
wood
practical: investigate how well different metals conduct heat
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
what is convection
the transfer of thermal enegy through fluids but he upward movement of warmer, less dense regions of fluid.
practical: investigating convection currents
put potassium manganate in water
how does a convection current work
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.
how does a convector heater work
cold air drawn in at bottom, heating elements inside the vent and then warm air is pushed out of the top.
how does an oven work
heating element is placed at the bottom of the oven. it relies on convection.
what are convection currents responsible for
on shore and off shore breezes (land and sea breezes)
on shore breeze
the land heats up quicker
off shore breeze
the land cools down quicker than the sea
what is thermal radiation
the transfer of energy by infrared waves
what are heat waves called
IR waves or IR radiation
what is thermal imaging
thy can detect objects giving out IR radiation
what are good reflectors of thermal radiation
highly polished, shiny surfaces or white surfaces
practical: investigate how well different surfaces radiate heat
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
if a surface is a good reflector of IR then it is
a poor radiatior of IR
what does the amount and type of energy radiated by a hot object depend on
surface texture, colour, and how hot it is
what does energy efficiency mean
using as much as possible of the energy we produce for the final purpose
how do the walls insualte a house
having an outer brick walland an inner wall made of thermal brick reduces heat loss by convection
how does the cavity or gap between the two walls help insulate a house
its wide enough for convection to circulate
what is the cavity or gap between the two walls filled with
glass fibre insulating wool is used to stop the convection currents in the air gap transferring thermal energy
outer brick wall is made of
bricks - good insulating properties, strong and will survive bad conditions
inner brick wall is made of
thermal bricks with good insulation properties. light, relatively cheap, and quick to work with.
how does double glazing work
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
what happens if the glass is too thick or thin in double glazing
if too thin then insulation effect is reduced, and if too thick then convection currets can circulate.
how else can houses be kept warm
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.
how much energy is lost through the walls and windes
walls 35%
windows 10%
how do human clothes keep us warrm
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.
what does wind do that causes heat loss
forced convection
what does hypothermic mean
their body temp starts to fall
how do animals stay warm
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
energy def
the ability to do work
energy unit
joules
work done (J) = W =
force (N) x distance moved (m)
F x d
1 joule of work done is transferred
when a force of 1N is applied through a distance of 1m in the direction of the force
what is GPE
gravitational potential energy
when does an object have a lot of GPE
when its high off the ground
GPE (J) =
mass (kg) x g x height (m)
m x g x h
KE (J) =
1/2 x mass (kg) x speed squared (m/s squared)
1/2 x m x vsquared
power unit
watts
power (watts) =
P =
work done (J) / time taken (s) W / t
practical: investigate your power output
weight yourself to find your mass, (W newtons)
measure the height of one stair
calculate your GPE on various stairs
density (kg/m cubed) =
ρ =
mass (kg) / volume (m cubed)
m / V
practical: investigate the density of solids
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
pressure (pascals) =
p
force (N) / area (sq m)
F / A
in which direction does pressure in liquids and gases act
equally in all directions as long as the liquid is not moving
what is the pressure exerted by the atmosphere on your body about
100 000 Pa
mass of liquid =
(area x height) x density
(A x h) x ρ
pressure difference (Pa) = p =
height (m) x density (kg/m cubed) x g
h x ρ x g
describe the structure and position of molecules in a solid substance
tightly packed
held in a fixed pattern or crystal substance by strong forces between them
vibrate around their fixed positions in the structure
describe the structure and position of molecules in a liquid substance
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
describe the structure and position of molecules in a gas substance
very spread out
no fixed positions and forces between them are very weak
move with rapid, random motion
what is specific heat capacity
the amount of energy required to increase the temperature of 1 kilogram of a certain substance by 1 degree celsius.
change in thermal energy (J) =
ΔQ
mass (kg) x specific heat capacity (c) x change in temperature (celsius)
m x c x ΔΘ
practical: investigate the specific heat capacity of a substance
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)
cause of gas pressure
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
boyles law
when he doubled pressure, the volume of gas halved. p as proportional to 1/V
p1V1 =
p2V2
why can gases be compressed
because the gas molecules are very spread out
if the gas is kept at the same temperature,
the average speed of the particles stays the same
what is temperature an indication of
the average speed of the particles
what did boyle make sure he did
conduct his experiment at a constant temperature because it has an effect on the pressure
what is -273 degrees
absolute zero
what does absolute zero mean
its the temperature where the pressure of a gas would be zero
temperature in K =
temperature in C + 273
temperature in C =
temperature in K - 273
p1 / T1 =
p2 / T2
T must be in K
Explain which colour is best at radiating thermal energy (2)
Black because it is a good emitter
Explain how convection heats a room (4)
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
suggest how a rradiator an be designed to help maximise heat transfer by convection (1)
maximise surface area
increase temperature of hot water
give the fossil fuels
coal, oil and natural gas
how have fossil fuels been formed
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.
how do fossil fuels harm the environment
by releasing greenhouse gases. these trap the suns heat in the earths atmosphere, causing global temp to rise.
what does global warming cause
changes in the worlds climate and melting of polar ice caps
order the fossil fuels in how much carbon dioxide they produce
coal, oil, natural gas
what happens when you burn coal and oil containing sulfur
it is converted to sulfur dioxide, which is then released into the atmosphere where it combines with water to form acid rain.
effects of acid rain
causes damage to people, plants and buildings.
can you remove sulfur and sulfur dioxide
yes but both are very expensive
what do nuclear reactors use to produce enrgy
uranium
does nucler power produce greenhouse gases
no itss vlean
adv of nuclear
no greenhouse or polluting gases
low cost per unit
disadv of nuclear
stations are expensive to build
problem of disposal of nuclear waste
radioactive accidents
how is electricity generated
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.
wood as an energy resource
renewable
but produces pollution and greenhouse gases
wood valuable if not burnt because it can be used in building or making furniture
how does HEP work
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.
how does tidal energy work
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
how does wave energy work
the continous movement of the surface of the seas and oceans is the result of a combination of tides and wind.
how does wind power work
wind turbine drive generators to provide electrical energy
disadv of wind power
can only be harvested in windy regions. they cause environmental damage, noise pollution and kill birds and bats.
what do photovoltaic cells do
transfer light energy directly to electrical energy
what effiency are PV cells
15%
adv of PV cells
provide a renewable energy resource that does not produce greenhoue gases
disadv of PV cells
could spoil countryside. farming land could be lost
solar panels absorb … and use it to….
thermal radiation to heat water
how are solar panels placed in the northern hempishere
face south and be angled.
how do solar panels work
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.
how can electricity be used to generate solar heating
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
how is geothermal energy produced
produced by the decay of radioactive elements like uranium.
what is geothermal energy used for
domestic heating and hot springs.
demand for energy
vaires all the time. (e.g. morning showers, tea in ad breaks etc)
why can nuclear power stations not be turned on quickly
a fission reaction must start and and heating up the core takes time
which is the quickest energy resource to turn on
HEP. they can also use extra electricity to pump water back into high level resevoirs.
availability of power station
can be started moe quickly than nuclear but still take time. coal takes even longer. gas fired stations respond the quickest
availibility of wind power
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
cost of nuclear
low maintance
high start up
high decomissioning
high disposal costs
cost of wind
lower start up
pau back time very long
