EX unit four: energy resources and energy transfer Flashcards
energy is neither created nor destroyed, it is….
converted from one form to another
energy stores
kinetic, gravitational, elastic potential, magnetic, electrostatic, nuclear, thermal and chemical
how is energy transferred by heating
energy is transferred from the hotter object to the cooler one, and the difference in temperature between them decreases.
how is energy transferred mechanically
energy can be transferred mechanically through the movement of the parts in machines, and when the motion or position of an object changes.
how is energy transferred electrically
when an electrical circuit is complete. internal energy stored in the battery is transferred to moving charged particles in the wire.
how is energy transferred by radiation
visible light, infrared, microwaves and radio waves are all forms of radiation, and are carried by waves (and are able to go through empty space).
what do sankey diagrams show
the energy transfers that take place in a system like a motor car. they should show that energy is conserved, but comes out in different forms.
total energy in =
total energy out
efficiency =
useful energy output / total energy input
what is efficiency usually given as, and how do you calculate it
a percentage by multiplying the equation by 100(%)
conduction
the transfer of thermal energy through a substance without the substance itself moving
how does conduction work
an increase in temperature means an increase in the average amount of kinetic energy of the molecules of the substance. this kinetic energy can be transferred from molecule to molecule in solids, passing the heat along.
why is conduction faster in metals
because electrons are free to move and can carry the energy much more quickly.
convection
thermal convection is the transfer of heat energy through fluids by the upward movement of warmer, less dense regions in the fluid.
how does convection work
when a fluid is heated it expands. this means that the density becomes lower, and the warmer fluid floats upwards as it is pushed out of the way by the colder and therefore denser fluid.
radiation
thermal radiation is the transfer of heat energy in the form of infrared waves. it is the only method of heat transfer through a vacuum.
dark surfaces ______ more radiation, so heat up faster.
absorb
matte surfaces _______ and _______ more radiation than light surfaces so heat up faster.
absorb
emit
dark surfaces _______ more radiation than light surfaces, so cool down faster.
emit
matte surfaces _______ more radiation than shiny surfaces so cool down faster.
emit
what does insulation in a house aim to do
reduce the rate of heat transfer between areas at different temperatures.
how to reduce heat transfer by conduction
use a vacuum, use air, use water.
how to reduce heat transfer by convection
use a vacuum, use trapped gas or liquid.
how to reduce heat transfer by radiation
use shiny surfaces, as they reflect radiation well.
work =
force x distance
what is work done measured in
joules (J)
what is energy measured in
joules (J)
what is energy
the ability to do work
gravitational potential energy =
mass x gravitational field strength x height
what is the symbol(s) for gravitational potential energy
GPE
what is the symbol for gravitational field strength
g
what is the symbol for height
h
what is gravitational field strength measured in
N/kg
what is height measured in
metres (m)
kinetic energy =
1/2 x mass x speed squared
what is the symbol for kinetic energy
KE
GPE at the start =
KE at the end
as height increases, does GPE increase or decrease?
increase.
power =
work done / time taken
what is the symbol for power
p
what is the symbol for work done
W
what is power measured in
watts
1 watt =
1 joule per second
the key process in the generation of electricity is turning mechanical energy into electricity with a generator. in many systems the kinetic energy is provided by a turbine driven by what?
a high pressure steam.
to produce the steam needed for the generation of electricity, there must be heat energy. where does this come from
geothermal energy, solar heating, controlled nuclear fission and fossil fuels.
what is geothermal energy
it is a naturally occuring energy produced by the heat of the earths core - this energy is accessible in places where volcanic activity is frequent.
what is solar heating
(it is more frequently used for the direct heating of water) but with the use of focusing mirrors it is possible to heat water for high pressure steam production.
what is controlled nuclear fission
it is a non-renewable resource (but will not run out for centuries) and there are problems with storing the radioactive waste securely and safely for a long time, inolving greenhouse gases
what are fossil fuels
they include oil, gas and coal. they’re non-renewable and produce greenhouse gases.
how can electricity be produced by renewable means
tidal power and wave power, wind power, solar power and hydroelectric power.
how does tidal and wave power to generate electricity work
barriers across tidal estuaries harness the kinetic energy of the sea, which drives water turbines as the tide comes in. the water trapped behind the dam can then be used, to drive turbines once the tide goes out.
how does wind power to generate electricity work
windmills harness the kinetic energy of the wind and converts it into other useful forms. the pressure variations in the atmosphere come from the sun.
how does solar power to generate electricity work
as a direct source of heat, and can be used with solar heat exchangers to provide hot water for domestic use.
how does hydroelectric power to generate electricity work
they convert the GPE of water in mountain lakes and reservoirs to electricity.
what are factors to consider when deciding the choice of energy used to generate electricity
cost (installation and maintenance), renewable/non-renewable, greenhouse gas emissions, supply and demand (can it be turned on and off to meet demand for e.g water), environmental impact and location.
