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Homework Help: Battery charged by a generator

  1. Apr 8, 2010 #1
    1. The problem statement, all variables and given/known data
    a generator of e.m.f 20V and internal resistance of 0.5 ohm is used to charge a car battery of emf 12V and internal resistance 0.10 ohm.They are connected in series together with a resistance R whose value is adjusted to give a charging current of 2.0A.

    I was asked to calculate
    a) value of R
    b) power of generator
    c) total rate of dissipation of electrical energy
    d) rate at which the battery stores chemical energy
    e) efficiency of the whole operation

    2. Relevant equations
    emf = I(R+r)

    3. The attempt at a solution
    i tried combining the 2 emfs and it sounds really funny, so i tried subtracting instead and still can't ring a bell.

    How exactly can i calculate the rate at which a battery stores chemical energy?
    anyone kindly provide me with an appropriate formula thanks.
    better yet explain the whole question so i can answer other similar questions which caused me the same headaches...=S
  2. jcsd
  3. Apr 8, 2010 #2


    User Avatar
    Homework Helper
    Gold Member

    Hello cyy91

    As a first step, draw out the diagram for this configuration. Seeing the diagram visually might make this problem seem a little easier.

    You need to calculate the power flowing into the battery's emf section (hint: it involves the battery's emf and the current flowing through it [albeit in the reverse direction as normal] :wink:).

    I think that once you start with the diagram, and work through what components are dissipating/using what power, things will fall into place. :cool:
  4. Apr 9, 2010 #3
    thx fr da help collinsmark...truly helps...:approve:
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