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I got this question in a homework from a teacher of mine:

"A car battery with a 15.0 V emf and an internal resistance of 0.0430 is being charged with a current of 62.5 A. What is the potential difference across its terminals?"

I've tried nearly every formula I know on it. EMF = IR + Ir gives me:

15.0 = (62.5 x R) + (62.5 x 0.0430)

15.0 = (62.5 x R) + 2.6875

62.5 x R = 12.3125

R = 0.197

If I then use that value in V = IR I get:

V = 62.5 x 0.197 = 12.3125

I tried that answer but it's incorrect...please, this is driving me nuts! Can anyone help me out? Does this seem like an incredibly hard question for a 16 year old?!?!?!

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# Homework Help: EMF related question, I'm totally stuck

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