1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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

    Born2bwire

    User Avatar
    Science Advisor
    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.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook