Calculating Battery Internal Resistance: V=IR Method

[accol]

1. A battery is manufactured to have and emf of 24V, but the terminal voltage is only 22V when the battery is connected across a 7.5ohm resistor...what is the internal resistance of the battery?




3. Ok I have the answer already which is .68ohm...but I can't find a way to get to it. At first I tried V=IR or 24=I*7.5 and then plugged that answer into the same equation but with the voltage of 22. I also tried the opposite way. That answer didn't work.

I also tried subtracting the volts from each other to get .27R. Can someone please tell me what I am doing wrong?

 

[Doc Al]

Answer these questions:
What's the voltage drop across the internal resistance?
What's the current through the circuit?
Combine these two answers to find the internal resistance.