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Homework Help: Current Elec.

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data
    My textbook says that the power delivered by the battery to external resistance network will be maximum when the external resistance equals the internal resistance? Why is it so?
    p = I^2 * R, so greater the external resistance, greater the power(even if it exceeds internal resistance)

    2. Relevant equations
    P = VI ;)

    3. The attempt at a solution
    Clueless about this one.
  2. jcsd
  3. Oct 6, 2009 #2


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    Homework Helper

    In the circuit the current is written as
    I = E/(R + r) where E is the emf of the battery and r is the internal resistance of the battery.
    So P = I^2*R =[ E^2/(R + r)^2]*R
    The power delivered by the battery depends on the external resistance. So find
    dP/dR and equate it to zero to get the condition for maximum power delivery
  4. Oct 6, 2009 #3
    Thanks a lot. :cool:
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