Accumulator Battery Internal Resistance & Charger Potential: A Doubt

[vikcool812]

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!

 

[Born2bwire]

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.