Energy Matters Answers.



  1. a) Fossil fuels are the name given to coal, oil, gas and petrol. These fuels were formed over millions of years. The dead matter being transformed from a dead tree into coal! It is amazing to realise that the energy from the sun captured by those trees millions of years ago is probably being used to run your computer at this exact moment.
    b) These fuels are finite because there is only a limited supply on this planet. So in the future this planet will run out of fossil fuels in much the same way as you run out of cornflakes!
  2. Solar, wind, waves and hydro are all examples of renewable energy sources. But as the table below shows they have their advantages and disadvantages.

    Energy Source Advantages Disadvantages
    Solar Always present during the day Not practical for countries like Scotland that don`t have much sunshine.
    Wind Wind turbines are now supplying electricity to small farms etc. Wind can be variable and some say the wind turbines are unsightly and too noisy.
    Waves Around the coasts there always are waves! Countries like the British Isles could have miles of tidal power stations. Research is currently ongoing to find an efficient system that can change the to and fro of the wave into electrical energy.
    Hydro You can use this power station at any time.Doesn`t need a long time for the electricity to come online. Need mountains and lots of rain. Scotland has it all!

  3. Find out how many 200kW you can get out of 2,000MW.
    Number of wind turbines needed = 2,000MW / 200kW
    this is the same as 2,000,000,000 / 200,000 = 20,000.
  4. Use the Potential Energy formula… Ep = mgh
    Put the numbers in to give
    Ep = 3 x 1010 x 10 x 200
    This gives a value of Ep = 6 x 1013J
    But the hydro power station is only 80% efficient.
    So the Energy that can be used from the dam = 80% of 6 x 1013J
    i.e. energy available = 0.80 x 6 x 10 13J
    = 4.8 x 1013J
  5. The block diagram for the power station is shown below:
  6. a) The voltage in the secondary is increased because this will in turn reduce the current flowing .And when less current flows in the secondary there will be less power losses due to the heating effect of the current.
  7. Use the formula P = I2 R putting the numbers in gives
    P = 402 x 400
    P = 640,000W per kilometre.
  8. Use the Energy formula E = cmT.
    The change in temperature is 100C - 25C = 75C
    Put the numbers into the equation to get E = 4,200 x 0.3 x 75
    This gives a value of E = 94,500J
  9. To answer this problem you need to calculate the energy needed to raise the water to boiling point , that is 100C.
    You do this by using the formula E = cmT.
    So energy needed to raise the water`s temperature is:
    E = 4,200 x 0.5 x 80
    E = 168,000J
    Now the energy needed to change 0.5kg of water at 100C to steam
    is found using the formula E = m x L
    where L is the specific latent heat of vaporisation
    which has a value of 2.3 x 106J/kg.
    So putting in the numbers E = 0.5 x 2.3 x 106
    So E = 1,150,000J
    So the total energy needed must be 168,000J + 1,150,000J
    = 1,318,000J
  10. Find the energy supplied by the water heater using E = Power x time make sure you put the time in seconds.
    3 minutes in seconds is 3 x 60 = 180seconds.
    E = 2000 x 180
    E = 360,000J
    Now put this into the formula E = cmT and find T.
    360,000 = 4,200 x 1 x T
    360,000 / 4,200 = T
    T = 85.7C
  11. Heat loss can be prevented by using roof insulation, double glazing and cavity wall insulation to name some common practices.
  12. When a liquid evaporates it takes heat in from the surroundings. Fridges work because evaporation takes energy from the surroundings which includes food kept in the fridge.
    A special liquid called freon is pumped through the pipes in the freezing compartment where it evaporates.
    The pump compresses the freon vapour back into a liquid. When this happpens the freon gives up the heat it took from the food. This heat is given through fins at the back of the fridge. See diagram below.




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