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Practice MCAT Question - Q43 - Answer!

A current of 20.0 A flows through a battery with an emf of 6.20 V. If the internal resistance of the battery is 0.01 Ohms, what is the terminal voltage?

A.  1.24 V
B.  6.00 V
C.  6.40 V
D.  31.0 V

The correct answer is (B). The Ir drop across the battery is the Joule heat produced:

Ir = (20 A)(0.01 V) = 0.20 V

Since the battery is producing current and not being recharged, the terminal voltage will be less than the emf by the Joule heat produced. This eliminates choices (C) and (D) immediately:

V = E - Ir = 6.20 V - 0.20 V = 6.00 V

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