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Physics (GCSE) Revision (Energy)

Energy cannot be created or destroyed but it can be . . . transferred from one form to another. For example: electricity into light.
When different parts of a substance are at different temperatures, energy is transferred from . . . high temperature to lower temperature. Heat flows from HOT to COLD (unless you are inside a fridge!)
When heat is transferred between solids the process is called . . . Conduction Vibrating atoms transfer kinetic energy - but free electrons in metals make them better conductors than non-metals.
Liquids and gases can flow and so can transfer energy by . . . Convection Hot fluid rises and is replaced by cooler fluid which sinks.
Energy can travel through a vacuum by . . . RADIATION How do you think sunlight reaches the Earth?
Hot bodies emit . . . INFRA-RED radiation. The hotter the body, the shorter the wavelength of radiation emitted.
Dark, matt (dull) surfaces are good . . . absorbers AND emitters of radiation. If HOT it emits - if COLD it absorbs.
Light, shiny surfaces are good . . . reflectors but poor absorbers or radiation. Shiny surfaces are also poor emitters - they keep heat in.
If you want to insulate your house you could . . . double glaze windows, fill cavity walls, insulate the loft with fibre glass. All these methods are used and more. Can you think of any?
When energy is transferred only some it of is useful, the rest is transferred in some non-useful way, usually as . . . heat, which is wasted. We are heating up the Earth with our waste energy.
The result of 'wasted' energy is that . . . the surroundings become warmer. This can be put to good use to heat homes - but it needs careful planning.
Energy lost from a system becomes increasingly spread out and it is therefore . . . difficult to use for further energy transfers. Low grade heat is not useful because the temperature difference is small.
If a device uses a high percentage of the energy supplied in a useful way we say it is . . . more EFFICIENT. NOTHING is ever 100% efficient!
The efficiency of a device is calculated by finding the ratio . . . Useful energy transferred/total energy supplied Usually less than 90%
Renewable energy resources are ones which can be . . . used over and over and will never run out. At least not within the expected lifetime of the Sun.
Non-renewable resources are ones which . . . are finite and which cannot be replaced during the lifetime of a human. Long term projects could regenerate some of our fuel supplies but not without significant cost.
Fossil fuels are those which . . . formed over millions of years deep inside the Earth. They are not going to be replaced - ever!
Coal, oil and natural gas are all examples of . . . Non-renewable resources - they are fossil fuels. The conditions which created them are unlikely to occur again on this planet.
Wind, wave, tidal, geothermal and solar energy are examples of . . . renewable resources. They depend on the energy stored in the Earth, Sun and Moon and will last as long as they do. The sun has over 5 billion years to live - we hope!
Most of the energy presently used by humans comes from non-renewable resources. We need to save them because . . . the more economical we are, the longer they will last. Until we find alternatives.
It is important to find alternative resources because . . . one day the fossil fuels will run out. We depend on oil for most of our transport.
Wood from trees is a renewable energy resource providing that . . . we replant at least as many trees as we cut down. The Amazon basin is being deforested at an alarming rate !
Electricity is a convenient, widely used energy source because . . . it can easily be transferred into other forms of energy. Think how many devices in your home use electricity.
In most power stations, energy from fuel is used to . . . heat water to produce steam. High pressure steam is used to drive turbines which are connected to generators.
Nuclear power stations use nuclear fuel, mainly . . . uranium and plutonium They also produce heat to make steam.
Renewable energy resources can also be used to produce electricity. These include . . . wind, waves, hydro-electric and geothermal energy. The technology needed is quite advanced in most cases.
Geothermal energy comes from . . . the decay of radioactive elements in Earth's crust which release heat. In volcanic areas hot water and steam rise to the surface and can be tapped.
Electricity can be produced directly from the Sun's radiation using . . . solar cells Passive solar heating can also be used to heat homes and offices.
Burning fossil fuels releases a gas called . . . carbon dioxide and also sulphur dioxide. Both bad for the planet.
The presence of CO2 in the Earth's atmosphere leads to . . . the Greenhouse effect Heat from the Sun is trapped and cannot escape to space.
The presence of SO2 in gases emitted by power stations causes . . . acid rain which destroys trees. The sulphur dioxide can be removed from the waste gases but this increases the cost of the electricity.
Nuclear power stations do not produce harmful gases. The main risk is from . . . the possible escape of radiation in the event of an accident. Chernobyl in 1987 was a serious accident which affected all of Europe.
The main disadvantage of nuclear power is . . . the radioactive waste which must be stored for thousands of years. No one wants it in their backyard.
Wind power is being developed in the UK. What are the main drawbacks? We need thousands of wind turbines and they look unsightly in the countryside. Also they need wind, which isn't always there when you need it.
A tidal barrage across a river estuary can produce a lot of energy. Why don't we have lots of them? They are costly and destroy wildlife. There are not that many suitable rivers actually.
Hydroelectricity is a good way of producing cheap electricity. What are the drawbacks? You need suitably high mountain reservoirs and they change the landscape permanently. Whole villages have been flooded by damming rivers.
Why are coal-fired power stations running all the time? It takes too long to start and stop them. We need to top-up our electricity supply at peak times using HEP and gas turbines.
The most expensive way to produce electricity at present is by . . . solar cells. They have a high cost per unit but are suitable for remote locations.
Energy is normally measured in . . . joules 1 J is the work done when a force of 1N moves through a distance of 1metre in the same direction as the force acts.
When a force acts on an object, the work done is equal to . . . the energy transferred W = F x s
Work done by a force = force x distance moved in the direction of the force 1N x 1m = 1J
The rate at which energy is transferred is . . . power in joules per second
The unit of power is the . . . watt 1W = 1J/s
Power = work done / time taken or work = power x time
The energy stored in an object which has been lifted against the force of gravity is . . . gravitational potential energy which depends on the height
Gravitational potential energy = weight x change in vertical height weight = mg
Weight = mass x gravitational field strength 9 = 10 N/kg
The gravitational field strength at the surface of the Earth is approximately . . . 10 N / kg g = 10 N/kg
A body falling freely in Earth's gravity will accelerate at . . . 10 metres per second squared g = 10 m/s^2
The energy an object has because of its movement is called . . . kinetic energy energy of motion
Kinetic energy = 1/2m v^2 1/2 mass x speed squared
When energy is transferred from one form to another the total amount of energy is . . . conserved This can be difficult to believe when friction is acting - friction produces heat
How much energy dya need 2 hav ur MUM WEll As much as i can get..girl goes on ALL NIGHT!!!
Created by: J Thomson
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