MCAT Physics – Electrical Circuits
 by
 Feb 09, 2015
 MCAT Blog, MCAT Physics, MCAT Question of the Day
A circuit with a total resistance of R and a current of I consumes a total power of P across the resistor network. If the electromotive force denoted by ξ does not equal the terminal voltage, which of the following expressions best approximates voltage lost due to internal resistance?
 ξ
 ξ + IR
 ξ – I^{2}R
 ξ – P/I
Explanation
This question is testing your understanding of electrical circuits and the relationship between current, voltage, power, and resistance. The question stem assigns each of these variables to the circuit described. Additionally, the question stem states that the electromotive force does not equal the terminal voltage, which is the voltage consumed by the resistors. Therefore, the difference between the EMF (ξ) and the terminal voltage (V) will equal the voltage lost to internal resistance.
Internal resistance = ξ – V
Since that is not an option, you must consider what else V is equal to:
(1) V = IR
(2) V = P/I
Substituting (2) into the equation above gives you answer choice D.
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