Physics One Important Points

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  • Created on: 16-01-13 19:37
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Physics One Important Points
Infrared radiation can be detected by our skin and can travel in a vacuum; the hotter an object is, the more infrared
radiation that it can give out
Dark, matt surfaces are good absorbers and emitters of infrared radiation so will transfer energy faster and cool down
more quickly than a white, shiny object since these are better reflectors
Solid particles vibrate in fixed positions; liquid particles are in contact with each other but are not fixed so can move at
random; gas particles are random and move around much faster so can flow and has a much lower density
Conduction occurs in solids; this is the transfer of energy from particle to particle; particles gain kinetic energy, vibrate
more, more collisions, energy is passed on; metals are very good conductors due to their free electrons
Convection occurs in liquids and gases; this is the circulation of the liquid or gas when it is heated; expands as it's heated,
less dense so rises, warm fluid replaced by cooler fluid, convection currents cause transfer of energy
Evaporation occurs when a liquid turns into a gas; happens because most energetic liquid particles escape from surface
into air; kinetic energy is less so temperature of liquid increases; rate of this increased by bigger surface area, increase in
temperature, creating a draught
Condensation is when gas turns into liquid; usually only takes place on very cold surfaces like windows; rate of this
increased by increase in surface area and reducing temperature of the surface
The greater the temperature difference between the object and the surroundings, the faster it will lose energy; this
depends on the material its in contact with, the shape of the object and its surface area
Maximizing rate of energy transfer to keep it cool; good conductors, painted dull black, air flow maximized
Minimize rate of energy transfer to keep it hot; good insulators, painted shiny white, air trapped in small pockets to
minimize convection
The greater the mass of an object, the more slowly the temperature will increase as it is heated; the rate of the
temperature change when heated depends on how much it has been heated, its mass and specific heat capacity; specific
heat capacity is the amount of energy needed to raise the temperature of 1kg of the substance by 1 degree
You want to minimize energy transfer outside of the home; loft insulation, cavity wall insulation (traps air in pockets),
double glazing (reduce conduction), draught proofing (reduce convection), foil behind radiators to reflect heat back into
the room; the lower the u-value, the better the material is as an insulator
Energy exists in different forms but only some can be stored; objects above ground have gravitational potential energy
and when they fall this is transferred into kinetic energy
Energy cannot be destroyed, it can only be transferred into another form of energy; the conservation of energy means the
energy at the start must be the same as the energy that is used up
Machines transfer energy from one form into another to make the energy useful however some of the energy is wasted;
eventually useful and wasted energy gets transferred to the surroundings as heat energy; the more spread out the
energy is, the harder it becomes to transfer
Energy is measured in Joules (J); energy supplied into a machine is known as input energy; the less energy the machine
wastes, the more efficient it is; no appliance is 100% efficient apart from an electric heater which transfers all its energy as
Electrical appliances convert electrical energy into a useful form of energy
The power of an appliance is how much energy it transfers and is measured in Watts (W); power is the energy per second
Cost effectiveness depends upon certain factors (cost of buying, cost of installing, cost of running, maintenance,
environmental costs, and interest charged on loan to buy the product); as many households want to cut down on their
energy bill, they often will buy newer appliances and install devices which reduce energy loss like insulation in their
In power stations water is heated to make steam which turns a turbine which is attached to an electrical generator to
produce electricity; this energy can come from fossil fuels; hot gases can also do this process and this causes electricity to
be produced much faster than other methods; biofuels are renewable sources of energy; nuclear power uses nuclear
fission reactions which uranium atoms are split, releasing lots of energy but radioactive waste is produced
Energy from waves, wind and tides is all renewable; wind and water can drive turbines which are linked into an electrical
generator; tidal power traps water at high tide then releases it at low tide to drive turbines to make electricity
Solar energy is renewable and the source of energy is free but not much energy is produced; this energy is used to heat
the water and produce steam in solar power towers but in the home is just used to heat up water; geothermal energy
comes from inside the earth due to the decay of radioactive material, cold water is driven down into the earth and is
heated to form lots of steam which then turns turbines so electricity is produced
Coal, oil, gas and uranium are not renewable sources so will eventually run out however they provide very reliable ways
of making electricity at the moment; there are advantages and disadvantages to every method used to produce
electricity at the current moment
Electricity in the UK is distributed throughout the National Grid system; it's made up of many cables and pylons which
transfer electricity; power stations produce electricity at 25000V but the National Grid increase the voltage using
transformers to 125000V then back to 230V; they increase it so that less of the energy is wasted as it travels a very long

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A constant amount of energy is always being produced known as the base load however demand can increase so some
power stations must work harder (gas-fired, pumped storage and renewable) to keep up with demand; if energy is
demand is low, stations will store the energy for future use
Waves can transfer energy and information; the direction of travel of wave is the direction information is transferred; in
transverse waves the vibration of particles is perpendicular to the direction the wave travels; in longitudinal waves…read more


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