SAT Subject Physics Practice Question 483: Answer and Explanation

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Question: 483

14. An electric circuit is composed of a pair of parallel 30 ohm resistors in series with a 9 ohm resistor. The current through the 9 ohm resistor is .25 A.What is the voltage applied to the circuit?

A. 1.5 V
B. 3 V
C. 6 V
D. 12 V
E. 24 V

Correct Answer: C


The correct answer is (C). To solve the problem you must first find the equivalent resistance of the two parallel resistors. The resistors are the same value; so divide 30 ohms by 2, which gives a value of 15 ohms. Add 15 ohms to the 9 ohms in series with the parallel resistors for a total resistance of 24 ohms. The voltage is equal to the current multiplied by the resistance, Ohm's Law. (24Ω)(.25) = 6 V.

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