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Josh C
#1 Posted : Sunday, August 07, 2011 8:08:54 PM
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Hello! could someone please explain this one to me?
A battery in a circuit had an electromotive force given by e, and an internal resistance of R. the battery provides a current I to the circuit. What is te terminal voltage of the battery
A) e
B)e- Ir
c) E=ir
d)e=i^2r
What on earth is terminal voltage?
correct ans is B)... although i'm not sure why... it makes intuitive sense that the total voltage generated would = pure voltage (e) - battery's internal resistance. but whats with the current thrown into the mix? is terminal voltage the net voltage from battery?
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asemac
#2 Posted : Monday, August 08, 2011 11:29:52 PM
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Hey Josh,

I think you pretty much figured it out. The terminal voltage is the net voltage that the battery provides. The electromotive force is the "pure" voltage. This question has to do with Kirchoff's second rule. Batteries usually have some internal resistance, so the actual voltage they provide is a bit less than the electromotive force. I think for most mcat questions you ignore this fact, unless, like in this question, they specificly ask for the terminal voltage or tell you to use the terminal voltage in the question.

They give you current because V=IR, and you need to mutiply the voltage by the internal resistance to get V, and subtract V from e to get your terminal voltage.

I hope that wasn't too confusing. Look in your Physics CC on page 103, it explains electomotive force, and Kirchoff's rules.
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