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    Just did the June 2003 Physics unit 4 paper (AQA b) and I made a mistake on what appeared to be a simple question, and I dont know why.

    "A turbine is linked to a generator that produces 800MW of electrical power. Calculate the efficiency of conversion of the internal energy of the steam into electrical enrgy."

    I thought efficiency = output/input

    From part (a) you know that 3.53GW is used to heat the water, so

    efficiency = 800E6/3.53E9 = 22.7%

    but apparently the answer is 18.5% (?). It says eff = 0.8/(0.8+3.53)

    I dont understand why!
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    Its the useful energy divided by the total energy thats been produced.
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    (Original post by queen-of-pain)
    Its the useful energy divided by the total energy thats been produced.
    OK that would make sense but in the text book it says

    efficiency = useful power output / power input

    Isn't power input is different from total produced?
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    Your textbooks defines it more generally, "total energy thats been produced" is a bit ambiguous.

    I don't understand why the useful power output would be used in the part of the equation that should represent the total power input.
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    (Original post by Goat)
    "A turbine is linked to a generator that produces 800MW of electrical power. Calculate the efficiency of conversion of the internal energy of the steam into electrical enrgy."

    I thought efficiency = output/input

    From part (a) you know that 3.53GW is used to heat the water, so

    efficiency = 800E6/3.53E9 = 22.7%

    but apparently the answer is 18.5% (?). It says eff = 0.8/(0.8+3.53)

    I dont understand why!
    From part a are you getting the energy lost when the steam re-cools ar the actual energy used to heat it?
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    (Original post by Golden Maverick)
    From part a are you getting the energy lost when the steam re-cools ar the actual energy used to heat it?
    Its the energy lost by the steam when is condensed by cold water.
 
 
 
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