ENERGY

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 

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 

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 

MOST POWER STATIONS USE STEAM TO DRIVE A TURBINE

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 

• 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 

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 

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 

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 

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

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 

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 

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 

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  

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 

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

• 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

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

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