A battery has internal resistance r = 1 mΩ and provides a 2 A current to the circuit. If the terminal voltage is 3 V, what is the electromotive force of the battery?
a) 2 mV
b) 2.998 V
c) 3.002 V
d) 3.004 V
Explanation
Electromotive force of a battery is equal to terminal voltage plus Ir, or the product of the current and the battery’s own internal resistance. As the question states, the terminal voltage is 3 V, so choices A and B (both less than 3 V) must be wrong. The “Ir” term can simply be calculated by multiplying 2 A and 1 mΩ, or 2 A and 0.001 Ω. This yields 0.002 V, which (when added to 3 V) gives us 3.002 V.
a) This choice is just v = ir, the voltage to the circuit without terminal voltage.
b) This is the terminal voltage minus (not plus) the voltage to the circuit.
c) This correctly represents the terminal voltage plus the voltage to the circuit.
d) This is terminal voltage plus I2r (circuit power) rather than circuit voltage.
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.
Create your Free Account to access our MCAT Flashcards
