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Emf continued

  1. Aug 18, 2009 #1
    This is in continuation to https://www.physicsforums.com/showthread.php?t=330495
    The question that initiated my doubt reads this -- " the internal resistance of an accumulator battery of emf 6V is 10 Ohm when fully discharged . as battery gets charged up , its internal resistance drops to 1 Ohm , . the battery when discharged is connected to a charger which maintains a constant potential of 9V . Find I when a)connections are just made b) when it is completely charged . "
    ans for 1st part is 0.3V (OK), but ans for b is 3V , , here they are treating the emf const. isn't it wrong , Pls. help!!!!!!!
  2. jcsd
  3. Aug 18, 2009 #2


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    Gold Member

    That seems correct. The equivalent circuit of a battery is a voltage source in series with a resistance. They have given you that the battery is now fully charged with an applied voltage of 9 V across the terminals. Thus, the battery now has a voltage of 6 V and an internal resistance of 1 Ohm. This works out to 3 A.

    By the way, they are asking for current, so the units are amps, not volts.
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