SAT Subject Physics Practice Question 90: Answer and Explanation

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Question: 90

8. Two resistors, A and B, are in series in a circuit that carries a nonzero current. If the resistance of Resistor A is 4 times greater than the resistance of Resistor B, which of the following correctly compares the currents through these resistors (IA and IB, respectively) and the voltage drops across them (VA and VB, respectively)?

A. IA = IB and VA = VB
B. IA = IB and VA = 4VB
C. IA = IB and VB = 4VA
D. IA = 4IB and VA = 4VB
E. IB = 4IA and VB = 4VA

Correct Answer: B


Resistors in series always share the same current, so we can eliminate D and E. Now, using Ohm’s law, V = IR, we see that if I is constant, then V is proportional to R. Since RA = 4RB, we know that VA = 4VB.

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