SAT Subject Physics Practice Question 594: Answer and Explanation

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Question: 594

5. Two different light bulbs are in a DC circuit powered by an 18 V battery as its power source. The two bulbs are rated at 4.5 watts (B1) and 6.75 watts (B2) each. What are the resistances of the two light bulbs (B1) and (B2)?

A. B1 is 48 Ω, and B2 is 72 Ω.
B. B1 is 72 Ω, and B2 is 48 Ω.
C. B1 is 2.67 Ω, and B2 is 4 Ω.
D. B1 is 4 Ω, and B2 is 2.67 Ω.
E. B1 is 20.25 Ω, and B2 is 45.56 Ω.

Correct Answer: B


The correct answer is (B). The resistance is calculated by using the power equation, R = V2/P. The solutions are:

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