Science P1

  • Created by: Natalie
  • Created on: 29-05-17 19:30

Energy

Energy: the ability to do work

Energy conservation: energy cannot be created or destroyed, only changes form

Energy dissipation: energy spreads out to the surroundings (often as heat (least useful form))

Efficiency: the difference between the amount of energy usefully used and the amount it produces

Efficiency can never be 100% because some is always dissipated to the surroundings

Closed System: where no object or energy can enter or exit. this means energy transfers will occur but no energy will leave the system --> the net change in energy will be zero

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Energy stores

Kinetic energy:

  • Movement = energy in an objects kinetic energy store
  • the greater the mass and speed...
  • the greater the kinetic energy

Gravitational potential energy:

  • work used to lift an object transfers to potential energy
  • the heavier, higher and...
  • greater the strenght of the gravitational field...
  • the greater the kinetic energy

A falling object transfers Eg -> Ek. Air resistance slows it down so some energy will be dissipated meaning the velocity will not be as high as calculated at the base of the fall

Elastic energy:

  • if the limit of proportionality is exceeded the object will not return to its original shape
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Power

Power: the rate of energy transfer

1 Watt = J/s

1 KW = KJ/s (1000J/s)

kilowatt hour = amount of KW x number of hours

The object with the greatest power will run out quickest

The object with the greatest power will transfer the same energy quicker.

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Specific heat capacity (c)

The amount of energy needed to change the temperature of 1kg by 1⁰C.

  • Unit is J/kg⁰C
  • EΔ = m x c x Δθ
  • Energy transferred = mass x specific heat capacity x temperature change
  • J = kg x J/kg⁰C x ⁰C

Experiment:

  • 1) get a block of the solid material with 2 holes in (one for heater one for thermometer)
  • 2) measure the mass of the block and record. wrap it an insulating layer to reduce heat loss
  • 3) measure the initial temperature of the block, record then set up a circuit to the heater. set the power supply to be 10 V. start the stopwatch
  • 4) take readings of the temperature every minute
  • 5) calculate the power supply of the heater using P = A x V
  • 6) calculate the energy transferred to the block using ET = P x T
  • 7) calculate the specific heat capacity using EΔ = m x c x Δθ
  • 8) repeat the experiment for all metal blocks
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Reducing energy wasted

Friction ® lubricants (oil)

Air resistance ® streamlined

Noise ® reduce vibrations/tighten loose parts

Heat loss ® insulation

Electrical resistance in wires ® low resistance wires

 Sankey diagram showing energy usefully used and energy wastedtotal electrical energy is 100 j, 90 j is transferred as heat energy and 10 j transferred as light energy (http://www.bbc.co.uk/schools/gcsebitesize/science/images/14_1_efficiency.gif).

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How to reduce heat loss in your home

Heat loss can be reduced in the home by:

  • using cavity wall insulation, double glazing and carpets. These reduce the amount of heat loss through conduction. 
  • introducing roof insulation and draught excluders. These reduce the amount of heat lost through convection. 
  • using shiny surfaces such as aluminium foil between the wall and the radiatior. This reduces the amount of heat loss through radiation.

Conduction is through solids for example windows, doors, walls etc. Hot particles collide faster and during collision transfer energy away to where it is not needed (the solids such as walls etc).

Convection is through air and liquids (fluids). This is a cycle where air particles are heated, rise, cool then sink. The hot particles move away (upwards) from where they are needed. 

Radiation is energy waves lost through walls and the roof. Dark, matt surfaces are better at giving out thermal radiation and light, shiny surfaces are better absorbers of thermal radiation.

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Energy resources

Renewable: energy that will never run out or be used up

  • solar
  • wind
  • wave
  • hydro-electricity
  • biofuel
  • tide
  • geothermal

Non-renewable: energy that will eventually run out or be used up

  • coal
  • oil
  • natural gas
  • nuclear
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Solar and wind

Solar: solar cells convert the suns energy into electricity

  • can be multi-used (a field with solar cells can also be used for sheep grazing)
  • no pollution (except to make)
  • very reliable (only in daytime)
  • still cost effective in cloudy countries (Britain)
  • can be used on a small or large scale
  • cant increase the power output when on high demand
  • inital costs are high
  • no energy produced at night or when cloudy

Wind: wind turbines spin a generator which produces electricity

  • no pollution (except to make)
  • can be multi-used (a field with wind turbines can also be used for cattle)
  • reliable (except when not windy)
  • inital costs are high
  • potential problems of no wind or wind being too strong
  • disliked because noise and visual pollution
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Wave and HEP

Wave: turbines are moved by the waves, spin generators which produce electricty

  • no pollution
  • useful on small islands/on small scales
  • unreliable (waves die out when wind drops)
  • initial costs are high
  • cannot produce energy on large scale
  • disturb seabed and habitats of marine animals
  • spoil the view and hazardous to boats

Hydro-Electric Power: falling water turns turbines that spin generators which produce electricity

  • no pollution
  • can produce immediate response to an increased demand
  • very reliable (except in countries with drought potential) 
  • good for small scale in remote areas
  • valley has to be flooded
  • destroys habitats and homes/buildings
  • inital cost is high
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Biofuel and tide

Biofuel: use plant waste or animal dung and can be burnt to produce electricity like fossil fuels

  • renewable only if plants replaced at same rate as used
  • fairly reliable as crops take relatively short time to grow
  • can be continuously produced and stored to meet energy demand
  • cost to refine is very high
  • uses space and water that could be used for food crops
  • sometimes forest is cleared to make space. this destroys habitats
  • burning biofuels produces greenhouse gases

Tide: tidal barages let tide through turbines which spin generators which produce electricity

  • no pollution
  • reliable (tides happen twice a day without fail)
  • no fuel costs, minimal running costs
  • spoils view and alters habitat of animals eg wading birds
  • 4 times a day the water level is the same height both sides - no energy produced
  • less energy produced when low (neap) tides
  • inital costs are high
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Geothermal, coal, oil and natural gas

Geothermal: water heated underground produces steam which spins generators which produce electricity

  • reliable
  • does little damage to the environment
  • can be used to generate electricity or heat buildings directly
  • potentially infinite source of energy
  • not many suitable locations
  • cost is very high compared to amount of energy produced

Coal, oil and natural gas:

  • known as "fossil fuels" because they were formed millions of years ago from dead plant and animal matter buried underground
  • they are reliable, cheap and can respond to changes in demand 
  • when burnt to produce fuel, they give off harmful greenhouse gases which pollute the atmosphere
  • they are running out and if no new stock is found may have disappeared within a few hundred years
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Nuclear... and about the public

  • nuclear power uses non-renewable sources such as uranium.
  • generating the power is clean but the nuclear waste is very dangerous, difficult and expensive to dispose of safely.
  • the fuel (uranium etc) is relatively cheap, but the overall cost of nuclear power is high due to the cost.
  • nuclear power always carries the risk of a major catastrophe as radiation is very harmful to humans.

People dont want to use more renewable energy because:

  • renewable power plants cost money. many people cant or dont want to pay this
  • there are arguments where to put things like wind turbines, solar panels etc.
  • scientists dont have the power to make people, coompanies or governments to change altough they can give advice and have a lot of scientific evidence

people do want to use more renewable energy because they know how damaging non-renewable is. also because they are aware that non-renewable will eventually run out and want to get by without non-renewables before this happens. there is also a lot of pressure from other countries and the public for governments and businesses to become renewable.

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