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Homework Help: Nuclear reaction/binding energy problem? Year 11 physics, so its fairly simple.

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data

    In the near future nuclear fusion reactions such as the one shown below may be used to produce electrical power.

    2 4
    2 H ----> He + energy
    1 2

    Physicists have suggested that 50 MW of energy will be sufficient to satisfy the energy needs of these industrial areas. If the nuclear reaction above is only 30% efficient, what mass of deuterium fuel will be needed per day.

    atomic mass (21)H = 2.024202 amu and of (42)H = 4.002603

    2. Relevant equations

    3. The attempt at a solution

    I'm in a state of panic right now. I have an exam tomorrow morning and don't get nuclear physics, it really just confuses me :(

    Any help at all is appreciated. Please. Please. Please. I'm not one for begging but... please. (Please).

    Thanks :)

    My feeble attempt:

    Find mass defect: H - H = 1.988501
    * 1.6606*10^-27
    = 2.1198 * 10^-27

    E = mc^2
    = 2.1198*10^-27 * (3*10^8)^2
    = 1.9078 * 10^-10 j

    Joules needed per day = 50*10^6 * 24 *60*60
    = 4.32 *10^11

    reactions per day =
    4.32*10^11 / 1.9027*10^-10
    2.26 * 10^21

    total mass needed = 2.014 * 2.26*10^21
    4.56 * 10^21 amu

    I know im probably wrong. I have no idea what im doing. Its all guessing and confusion. I don't even have the answer to this problem, and its a revision sheet. Ugh. Im going to fail this exam so hard.

    If you help me i will be eternally grateful. :)
  2. jcsd
  3. Nov 16, 2008 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The mass defect would be the difference in mass of the reactant and the product nuclei. The reactants are 2 deuterium nuclei and the product is one He nucleus. So what is the change in mass (and, hence, the amount of energy released) per reaction?

    Use that figure as the mass defect and the rest is fine.

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