MCAT Physics Question 81: Answer and Explanation

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Question: 81

6. Given that R1 = 20 Ω, R2 = 4 Ω, R3 = R4 = 32 Ω, R5 = 15 Ω, and R6 = 5 Ω, what is the total resistance in the circuit shown below?

  • A. 0.15 Ω
  • B. 6.67 Ω
  • C. 16.7 Ω
  • D. 60 Ω

Correct Answer: B

Explanation:

The fastest way to tackle these kinds of questions is to simplify the circuit bit by bit. For example, notice that R3 and R4 are in parallel with each other and are in series with R2; similarly, R5 and R6 are in series. If we determine the total resistance in each branch, we will be left with three branches in parallel. To start, find the total resistance in the middle branch:

Next, take a look at the total resistance in the bottom branch:

R5+6 = R5 + R6 = 15 ? + 5 ? = 20 ?

The circuit can now be viewed as three resistors in parallel, each providing a resistance of 20 ?. The total resistance in the circuit is thus

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