- Created by: Benny52
- Created on: 25-02-19 20:00
Specific Heat Capacity
- More energy needs to be transferred to thermal energy store of some materials to increase temp. than others. Materials that need to gain lots of energy in thermal energy stores to warm up transfer lots of energy when cooling down - can 'store' lost of energy.
- Specific heat capacity = amount of energy needed to raise temp. of 1kg of substance by 1 degrees C.
- Change in thermal energy (J) =
- mass (kg) x specific heat capacity (J/kg degrees C) x temp. change (degrees C)
SEE PRACTICAL SHEET FOR PRACTICAL
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Energy Stores & Systems
- Types of energy stores: Thermal, Kinetic, Gravitational potential, Elastic potential, Chemical, Magnetic, Electrostatic & Nuclear. When energy transferred, energy stored in one of object's energy stores. Energy transferred mechanically - by force doing work, electrically - work done by moving charges, by heating, or radiation - light or sound.
- System - a single object or a group of objects. When it changes, energy is transferred into or away from system, between different objects in system of different energy stores. Closed systems - no matter or energy can enter or leave. Net change in total energy of closed system = 0.
- Energy can be transferred by heating. Energy transferred by heating to system's themal energy store, causing temp. rise. Can also be transferred by doing work. Work done = energy transferred. Done when current flows - work done against resistance in circuit, or by force moving an object.
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Kinetic & Potential Energy Stores
- Movement - energy in object's kinetic energy store. Energy transferred to it when objects speed up and away when object slows down. Energy depends on object's mass & speed. Greater mass and faster its going - more energy.
- Kinetic Energy = 1/2 x Mass x Speed (squared) Ek = 1/2mv(squared)
- Lifting object in gravitiational field needs work. Causes transfer of energy to gravitiational potential energy store of raised object. Higher object lifted - more energy transferred. Depends on mass, height & strength of gravitiational field.
- Gravitational Potential Energy = Mass x Gravitiational Field Strength x Height Ep = mgh
- Falling object - energy from gravitational potential energy transferred to kinetic energy store. For falling object when there's no air resistance: Energy lost from g.p.e store =energy gained in kinetic energy store. Real life - air resistance acts against falling objects - causes some energy to be transferred to other stores.
- Stretching or squashing object transfers energy to elastic potential energy store. As long as limit of proportionality hasn't been exceeded:
- Elastic Potential Energy = 1/2 x Spring Constant x Extension (squared)
- Ee= 1/2ke(squared)
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Conservation of Energy & Power
- Conservation of energy principle: Energy = transferred usefully, stored or dissipated -never created or destroyed. When energy's transferred, not all is transferred usefully. Some always dissipated. Dissipated energy - 'wasted energy'.
- Power = rate of energy transfer/doing work. 1 watt = 1 joule of energy transferred per sec.
- Power = Energy Trasferred / Time or Work Done / Time P = E/T or W/T
- Powerful machine one which transfers lots of energy in short time period.
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Reducing Unwanted Energy Transfers
- Objects being rubbed together - lubricants reduce friction between objects' surfaces. Usually liquids - flow easily between objects & coat them.
- When object heated, energy transferred to kinetic energy store of particles, causing them to vibrate more & collide. Collisions - energy transferred between particles' kinetic energy stores - conduction. Thermal conductivity = measure of how quick energy is transferred through material in this way. Higher = faster.
- If particles free to move, particles moving faster mean space between particles increase - density of heated areas decreases. As liquid & gases flow, warmer & less denser areas rise above denser, cooler areas - energetic particles move from hotter to cooler areas - convection.
- Preventing energy losses through heating: Thick walls made from material with low thermal conductivity - slower rate of energy transfer. Thermal insulation:
- Cavity walls - air gap in middle reduces energy tansferred by conduction through walls. Cavity wall insulation - air gap filled - foam - reduces energy transfer by convection.
- Loft insulation - reduces convection currents (cycle where air particles are heated, rising, cooling and sinking) created in lofts.
- Double-glazed windows - air gap.
- Draught excluders - reduce energy transfers by convection.
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- Less energy 'wasted', more efficient device is. Improve efficiency by insulating objects, lubricating them or making them more streamlined.
- Efficiency = Useful Output Energy Transfer / Total Input Energy Transfer or Useful Power Output / Total Power Input
- No device 100% efficient & wasted energy usually transferred to useless thermal energy stores, but electric heaters - all energy in electrostatic energy store transferred to 'useful' thermal energy stores.
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Energy Resources & Their Uses
- Non-renewable energy - fossil fuels & nuclear fuel. Fossil fuels - natural resources that form underground over million of years. Burnt to provide energy. Three main types: Coal, Oil & Natural Gas. Will all 'run out', damage environment & provide most energy.
- Renewable energy resources: Solar, Wind, Water waves, Hydro-electricity, Bio-fuel, Tides & Geothermal. Never run out. Most damage environment but less harshly than non-renewables. Don't provide much energy. Some unreliable - depend on weather.
- Fuel used for transport - petrol & deisel - cars - fuel from oil. Coal - steam trains - boils water to produce steam. Vehicles run on bio-fuels or mix of that and petrol or deisel.
- Energy resources - heating: Natural gas - heats homes - used to heat water - pumped into radiators throughout home. Coal - burnt in fireplaces. Electric heaters - use electricity from non-renewables. Geothermal heat pump - geothermal energy resources. Solar water heaters - uses sun to heat water - pumped into radiators. Burning bio-fuel or using electricity from renewables - used for heating.
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Wind, Solar & Geothermal
- Wind power - turbines in exposed places. Each has generator - rotating blades turn generator & produce electricity. No pollution but little from manufacture. Spoil view. Noisy. If wind stops of it's too strong - turbines stop - can't increase supply if extra demand. Initial costs - high, but no fuel costs & small running costs. No permanent landscape damage.
- Solar cells generate electric currents from sunlight. Used to charge batteries in calculators & watches - don't use much electricity. Often used in remote places - little choice & to power electric road signs & satellites. No pollution but lots of energy used in manufacture. Sunny countries - reliable in daytime. Still cost-effective in cloudy countries. Can't increase output with extra demand. Inital costs - high but after, energy - free & running costs tiny. Used to generate electricity on small scale.
- Geothermal power - energy in underground thermal energy stores - volcanic areas or where hot rocks lie near surface. Source of most - slow decay of radioactive elements - uranium, etc., deep inside earth. Free & reliable with no real environmental problems. Used to generatre electricity or heat buildings direct. Not many suitable locations for power plants & cost of building is high compared to amount of energy produced.
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Hydro-electricity, Waves & Tides
- Hydro-electric power - requires flooding of valley by building dam. Water allowed through turbines. No pollution. Flooding - rotting veg releases CH4 & CO2. Also loss of habitat or villages. Reservoirs - unsightly when dried up. Power stations in remote valleys reduce impacts. Provides immediate response to increased electricity demand. Reliable apart from droughts. Initial costs high but no fuel costs & small running costs. Useful for generating electricity on small scale in remote areas.
- Wave power - lots of small wave-powered turbines located around coast. Turbines connected to generator. No pollution. Disturbs seabed & habitat of marine animals, spoils view & hazard to boats. Fairly unreliable - waves die out when wind drops. Initial costs - high but no fuel costs & low running costs. Useful for small scale energy on small islands.
- Tidal barrages - big dams built across river estuaries - turbines in them. As tide comes in it fills up estuary. Water allowed out through turbines at controlled speed. Tides produced by gravitational pull of Sun & Moon. No pollution. Prevents free access by boats, spoils view & alter's habitat of wildlife. Reliable, but height of tides vary - lower - less energy. Doesn't work when water level is same either side of barrage. Initial costs - high but no fuel costs & low running costs.
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Trends in Energy Resource Use
- UK electricity use - increased - pop. grew, & people use energy for more things. Electricity use starting to decrease - more efficient appliances & more careful with energy use.
- Most electricity - fossil fuels & nuclear power. Trying to increase use of renewables.
- Burning fossil fuels - harmful for environment. People want to use renewables - lower effect. Non-renewables will run out. People think its better to learn to get by without before they run out. Pressure from other countries & public - governments introducing targets for using renewables - pressure on energy providers to build new plants that use renewables - wont lose business & money. Car companies - electric cars & hybrids.
- Building renewable plants - expensive - some energy providers reluctant, especially when fossil fuels = cost effective. Cost of switching paid by customers - bills or by government - taxes. Some people dont want to or can't afford to pay. Arguments where to put new plants - people don't want to live near. Some renewables not as reliable as fossil fuels, & others can't increase output on demand - combination of plants used - expensive, or research ways to improve reliability - lenghty & expensive. Personal changes - expensive - hybrid cars, solar panels.
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Bio-fuels & Non-renewables
- Bio-fuels - made from plant products or animal dung. Can be 1 of 3 states of matter & burnt to produce electricity or run cars. Supposedly carbon neurtal - only if plants grown at rate of burning things. Reliable - take short time to grow & different crops can be grown all year. Cannot respond to immediate energy demands - bio-fuels constantly produced & stored. Cost to refine bio-fuels - high. Some worry growing crops for bio-fuels mean not enough space or water for food crops. Some regions - large areas of forest cleared - room for bio-fuels - species lose habitats. Decay & burning of veg increases CO2 & MH4 emissions.
- Fossil fuels & nuclear energy - reliable. Enough to meet current demand - plants can respond quickly to demand changes. Running out. Set-up costs - high but running costs, not so expensive. Fairly low fuel extraction costs - fossil fuels cost effective.
- Fossil fuels - release CO2 into atmosphere when burnt - adds to greenhouse effect & contributes to global warming. Burning coal & oil - sulfur dioxide released - acid rain - harmful to trees, soils & ecosystems. Sulfur can be removed before fuel burnt, or emissions cleaned up. Coal mining - messes landscape. View spoilt by plants. Oil spillages - environmental problems, affecting mammals & birds living in & around sea.
- Nuclear power clean but waste - dangerous & disposal difficult. Nuclear fuel - cheap but overall cost = high - cost of plant & final decommissioning. Risk of major catastrophe.
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