Internal resistance of the battery and power dissipation

I got this question ( i won't include a lot of details because this is not the hw forum) where i need to calculate the power dissipation due to internal resistance. What i did is , i calculated total V and total R and I , then i treated the battery as a normal resistance ( eg. a 1kohm resistor , of course it has way less resistance ) , was that the right thing to do ?
Should the batteries be treated differently than resistors when it come to power dissipation?

sophiecentaur
Gold Member
There are many different ways of thinking about and calculating these things. But you end up learning shortcuts and some ways are a bit shorter; whatever suits you is good. When answering exam questions, it's always good to put all your workings in and annotate them briefly so you can get some marks even if your arithmetic is wrong. That internal resistor can be treated just the same as any resistor. (Most batteries are treated as if they have a pretty well fixed equivalent ohmic resistor inside them.)
If you want to do it that way, that's fine. Input V and total R gives current. Then Isquared times the appropriate R gives the power dissipated in the resistor.
Sometimes it's good to calculate things in more than one way and feel smart when you get the same answer each time.

There are many different ways of thinking about and calculating these things. But you end up learning shortcuts and some ways are a bit shorter; whatever suits you is good. When answering exam questions, it's always good to put all your workings in and annotate them briefly so you can get some marks even if your arithmetic is wrong. That internal resistor can be treated just the same as any resistor. (Most batteries are treated as if they have a pretty well fixed equivalent ohmic resistor inside them.)
If you want to do it that way, that's fine. Input V and total R gives current. Then Isquared times the appropriate R gives the power dissipated in the resistor.
Sometimes it's good to calculate things in more than one way and feel smart when you get the same answer each time.
i have this problem where there are 3 batteries in parallel
and one resistor , to calculate the power dissipation i used this formula from this site ( http://farside.ph.utexas.edu/teaching/302l/lectures/node62.html )(V^2*r/(r+R)^2)
will that work ? can i simply replace the r+R in his formula by the total resistance of the circuit?

sophiecentaur
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