ENERGY

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  • Created by: Sam
  • Created on: 29-05-13 16:27

ELECTRIC CURRENT AND POWER

ELECTRIC CURRENT: FLOW OF CHARGE ROUND A CIRCUIT

  • CURRENT: rate of flow of charge
  • VOLTAGE: electrical pressure giving a measure of energy transferred 
  • CONVENTIONAL CURRENT: positive to negative

A.C. KEEPS CHANGING DIRECTION BUT D.C. DOES NOT

  • Mains electricity is alternating current - reverses direction back and forth 
  • CRO shows current as a trace on a graph - a.c. trace = wave
  • Direct current always flows in the same direction - CRO trace = horizontal line
  • Voltage doesn't vary so neither does current
  • D.C. from batteries and solar cells

ELECTRICAL POWER: ENERGY TRANSFERRED PER SECOND

  • Electrical appliances convert electrical energy into other forms of energy 
  • Electrical power tells you how quickly it transfers electrical energy
  • Units of power are watts - the higher the power of an appliance, the more energy transferred every second
  • POWER = CURRENT X VOLTAGE 
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GENRATING ELECTRICITY

MOVING A MAGNET IN A COIL OF WIRE INDUCES A VOLTAGE

  • Called electromagnetic induction 
  • Magnetic field through the coil changes as magnet is moved - induces a voltage and a current flows in the wire
  • If you move the magnet into the coil the voltage and current are induced in the opposite direction from when you move it out
  • If you reverse the polarity the voltage and current are induced in the opposite direction
  • This can also be done by rotating a magnet in or near a coil of wire or rotating a coil of wire in a magnetic field

FOUR FACTORS AFFECT THE SIZE OF THE INDUCED VOLTAGE AND CURRENT

  • The STRENGTH of the MAGNET, the AREA of the COIL, the number of TURNS on the COIL, the SPEED of the movement
  • Faster turning also gives a higher frequency 

THIS IS HOW ALL GENERATORS WORK

  • Generate alternating current by electromagnetic induction by rotating a magnet or a coil of wire
  • Something's needed to do the turning
  • Dynamo: often used on bikes to power the lights. Magnet is rotated. It's attached to a wheel 
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NON-RENEWABLE ENERGY AND POWER STATIONS (1)

NON-RENEWABLE ENERGY RESOURCES

  • COAL, OIL, NATURAL GAS, NUCLEAR FUELS (URANIUM and PLUTONIUM)
  • They will all run out one day
  • They all damage the environment 
  • But they provide most of our energy 

ENVIRONMENTAL PROBLEMS WITH NON-RENEWABLES

  • Fossil fuels release carbon dioxide - coal the most, then oil then natural gas, adding to greenhouse effect - global warming 
  • Can be stopped by catching and burying underground - too expensive for wide use
  • Burning coal and oil releases sulfur dioxide - acid rain
  • Reduced by taking sulfur out before it's burned or cleaning up emissions
  • Coal mining makes a mess of the landscape, especially 'open-cast mining'
  • Oil spillages cause serious environmental problems
  • Nuclear power is clean but nuclear waste is very dangerous and difficult to dispose of
  • Nuclear fuel relatively cheap but overall cost of power high due to cost of building and decommissioning power plants
  • Nuclear power always carries the risk of a major catastrophe like Chernobyl 
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NON-RENEWABLE ENERGY AND POWER STATIONS (2)

MOST POWER STATIONS USE STEAM TO DRIVE A TURBINE

(http://revisionworld.co.uk/sites/default/files/imce/coal-fired-power-station2.gif)

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NON-RENEWABLE ENERGY AND POWER STATIONS (3)

NUCLEAR REACTORS 

  • Like most power stations where nuclear produces heat to make steam to drive turbines - difference in boiler
  • They take the longest of all power stations to start up. Natural gas takes the shortest 

(http://t2.gstatic.com/images?q=tbn:ANd9GcR5JsxSaaZ25UCLIIcjjKPzQb1qNWaLAjkpHiwxKdDnFlvoLR1aRA)

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USING RENEWABLE ENERGY RESOURCES (1)

  • Renewable energy resource will never run out
  • Most do damage the environment, but in less nasty ways than non-renewables 
  • They don't all provide much energy and some are unreliable as they depend on the weather

HYDROELECTRICITY 

  • Involves flooding a valley by building a big dam
  • Rain water is caught and allowed out through turbines 
  • There's a big impact on the environment because of flooding - possible loss of habitat
  • Big advantage - immediate response to increased electricity demand - more water can be let out through turbines to generate more 
  • Initial costs often high but there are minimal running costs and it's reliable 
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HYDROELECTRICITY

(http://images4.wikia.nocookie.net/__cb20080418165438/gcse/images/4/4d/Hydroelectric_power_plant.gif)

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USING RENEWABLE ENERGY RESOURCES (2)

WAVE POWER 

  • Waves can provide an up and down motion which can drive a generator 
  • Wave power is fairly unreliable - waves die out when the wind drops
  • Most electricity generated from wave power uses waves close to the shore
  • Waves further out are much more powerful - offshore wave farms are now being developed
  • It is never likely to provide energy on a large scale but can be useful for small islands 

TIDAL BARRAGES 

  • Big dams built across river estuaries with turbines in them
  • As the tide enters it fills up the estuary to a height of several metres
  • This water is then allowed through turbines at a controlled speed - drives turbine on the way in
  • Can only be used in a few most suitable estuaries but is a reliable energy source with the power to generate a significant amount of energy 
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WAVE POWER

(http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Wave%20power%20files/image013.jpg)

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TIDAL BARRAGES

(http://www.bettergreen.co.uk/images/Tidal%20Barrage%20Final.png)

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USING RENEWABLE ENERGY RESOURCES (3)

WIND POWER

  • Each turbine has its own generator inside it - the electricity is generated directly from the wind turning the blades which turn the generator 
  • No pollution 
  • They do spoil the view and can be very noisy
  • They only work when it's windy - not always possible to supply more electricity when there's an extra demand 

SOLAR CELLS 

  • Used to generate electricity on a relatively small scale 
  • Often used in remote places where there aren't many other ways to generate electricity, and in satellites 
  • Very reliable source in sunny countries but only in the daytime 
  • Solar power can still be cost-effective even in cloudy countries like Britain 
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SOLAR CELLS

(http://www.fsec.ucf.edu/en/consumer/solar_electricity/basics/images/F1_HowCellWorks_401x217.gif)

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USING RENEWABLE ENERGY RESOURCES (4)

GEOTHERMAL ENERGY 

  • Only possible in places where hot rocks lie quite near to the surface
  • Much of the heat comes from slow decay of radioactive elements, like uranium, deep inside the Earth 
  • Water's pumped in pied down to the hot rocks and it returns as steam to drive a generator 
  • This is brilliant 'free' energy with no environmental problems 
  • The big drawbacks are the high setup cost and the fact that there are very places where this is an economic option 

BIOMASS

  • Anything from farm waste, animal droppings and landfill rubbish to specially grown forests
  • Waste material is burnt in power stations to drive turbines and produce electricity 
  • Sometimes it's fermented to produce other fuels like 'biogas' or ethanol 
  • Plants grown to produce the waste would have absorbed carbon dioxide from the atmosphere
  • When the waste is burnt this is re-released
  • So, using biomass has no overall effect on atmospheric carbon dioxide levels - carbon neutral 
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GEOTHERMAL ENERGY

(http://www.epa.gov/climatestudents/images/4-1-5-geopower.gif)

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COMPARISON OF ENERGY RESOURCES

SETTING UP A POWER STATION

  • Many old coal- and oil-fired power stations are being taken out of use - often replaced by gas-fired power stations as quick to set up, still a lot go gas left and doesn't pollute as badly 
  • Several factors to consider when looking at options for new power stations: how much it costs, how long it takes to build, how much power it can generate etc 
  • Also trickier factors like damage to the environment and impact on local communities - very contentious issues so getting permission can be a long-running process and increase overall set-up time 

SET-UP COSTS

  • Renewable resources need bigger power stations than non-renewables for the same output - the bigger the more expensive
  • Nuclear reactors and hydroelectric dams need huge amounts of engineering to make them safe
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COMPARISON OF ENERGY RESOURCES (2)

SET-UP TIME

  • Affected by size of power station, complexity of engineering and planning issues - gas one of the quickest to set up 

RUNNING/FUEL COSTS 

  • Renewables usually have lowest running costs - no actual fuel involved 

RELIABILITY ISSUES 

  • All non-renewables are reliable energy providers 
  • Many renewable sources depend on weather - pretty unreliable in the UK
  • Exceptions are tidal power and geothermal 
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COMPARISON OF ENERGY RESOURCES (3)

ENVIRONMENTAL ISSUES

  • If a fuel is used - waste pollution and using up resources 
  • If it relies on weather - be in an exposed place where it sticks out
  • Atmospheric pollution - Coal, Oil, Gas, Biomass
  • Visual pollution - Coal, Oil, Gas, Nuclear, Tidal, Waves, Wind, Hydroelectric, Biomass 
  • Other problems - Nuclear (dangerous waste, explosions, contamination), Hydroelectric (dams bursting)
  • Using up resources - Coal, Oil, Gas, Nuclear 
  • Noise pollution - Coal, Oil, Gas, Nuclear, Wind, Biomass
  • Disruption of wildlife habitats - Hydroelectric, Tidal 
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COMPARISON OF ENERGY RESOURCES (4)

LOCATION ISSUES 

  • Solar - anywhere though the sunnier the better
  • Gas - anywhere there's piped gas (most of UK)
  • Biomass - anywhere 
  • Hydroelectric - hilly, rainy places with floodable valleys, e.g. Lake District, Scottish Highlands
  • Wind - exposed, windy places like moors and coasts or out at sea
  • Oil - near the coast (oil transported by sea)
  • Waves - on the coast 
  • Coal - near coal mines, e.g. Yorkshire, Wales 
  • Nuclear - away from people (in case of disaster), near water (for cooling) 
  • Tidal - big river estuaries where a dam can be built
  • Geothermal - fairly limited, only in places where hot rocks are near the Earth's surface 
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ELECTRICITY AND THE NATIONAL GRID

THE NATIONAL GRID 

  • Takes electrical energy from power stations to homes and industry 
  • Enables power to be generated anywhere on the grid and then supplied anywhere else
  • A high voltage or high current is needed to transmit the huge amount of power needed
  • Lots of energy is lost through heat in the cables with a high current 
  • Much cheaper to boost the voltage up really high and keep current very low 

PYLONS AND TRANSFORMERS 

  • Transformers and big pylons with huge insulators to get the voltage to 400 000V - still cheaper
  • Transformers have to step up alternating voltage at one end for efficient transmission and bring it back down to safe, usable levels 
  • Transformers have primary and secondary coils joined with an iron core
  • Voltage is increased using a step-up transformer - more turns on secondary coil 
  • Reduced with step-down transformer - more turns on primary coil 
  • PRIMARY VOLTAGE/ SECONDARY VOLTAGE =                                                           NO. TURNS ON PRIMARY/ NO. TURNS ON SECONDARY
  • Equation can be used either way up  
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ELECTRICITY AND THE NATIONAL GRID (2)

PROBLEMS

  • Power losses high - even at high voltage electricity transmission isn't very efficient 
  • High voltage is a risk to people 
  • Some people worried about the effects on longer-term health of people living near power lines - links with leukaemia have been suggested 
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ENERGY EFFICIENCY & COST-EFFICIENCY

INSULATING YOUR HOUSE

  • Saves money on heating bills but costs money to install 
  • The money you save will equal the initial cost - time it takes called payback time
  • After that money is saved every year 
  • Cheaper methods of insulation are usually less effective - save less money per year but they have short payback times - more cost-efficient
  • Payback time = inital cost/annual saving 
  • Low-energy and efficient appliances are cheaper to run but often more expensive to buy 

ENERGY 

  • Normally measured in joules or kilojoules 
  • Amount of energy an appliance uses depends on power and time left on:
  • POWER (W) = ENERGY (J)/ TIME (s)
  • Electricity meters record how much energy used in kilowatt-hours - amount of energy used by a 1kW appliance left on for 1 hour 
  • COST = POWER (in kW) X TIME (hours) X COST of 1 kWh
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WORK AND POWER

  • Whenever something moves something provides 'effort' to move it
  • That thing needs a supply of energy (fuel, food, electricity etc)
  • It does 'work' by moving the object - transfers energy it receives into other forms
  • Whether transferred 'usefully' or 'wasted' 'work is done'
  • Work Done (J) = Force (N) X Distance moved in the direction of the force (m)

POWER

  • 'Rate of doing work' - how much per second 
  • Powerful machine - transfers a lot of energy in a short space of time 
  • Power = Work done/ Time taken 
  • Measured in watts or J/s
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KINETIC AND POTENTIAL ENERGY

KINETIC ENERGY 

  • Energy for movement 
  • Kinetic Energy = 1/2 X mass X velocity^2
  • So the more something weighs and the faster it's going, the bigger its kinetic energy will be 

GRAVITATIONAL POTENTIAL ENERGY 

  • Gravitational Potential Energy = mass x g x height 
  • The proper name for g is 'gravitational field strength' and its units are newtons per kilogram (N.kg) - on Earth it is approximately 10 N/kg
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CONSERVATION OF ENERGY

THE PRINCIPLE OF THE CONSERRVATION OF ENERGY 

  • ENERGY can never be CREATED NOR DESTROYED - only TRANSFERRED from one form to another 
  • Energy is ONLY USEFUL when it's TRANSFERRED from one form to another 

CALCULATING THE SPEED OF FALLING OBJECTS

  • G.P.E is converted into K.E. when something falls - the further it falls, the faster it foes 
  • Kinetic energy GAINED = Gravitational potential energy LOST 

ENERGY TRANSFERS

  • Every time energy's transferred from one form to another, some energy is lost to surrounding - often as heat and sometimes sound 
  • Heat energy's transferred to cooler surrounding that become warmer - as heat is transferred to cooler surrounding, the energy becomes less concentrated - it dissipates 
  • According the Principle of Conservation of Energy total amount of energy stays the same - energy is still there but can't be easily used or collected back in 
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