MCAT Physics Question 78: Answer and Explanation

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Question: 78

3. The resistance of two conductors of equal cross-sectional area and equal lengths are compared, and are found to be in the ratio 1:2. The resistivities of the materials from which they are constructed must therefore be in what ratio?

  • A. 1:01
  • B. 1:02
  • C. 2:01
  • D. 4:01

Correct Answer: B

Explanation:

The resistance of a resistor is given by the formula

Thus, there is a direct proportionality between resistance and resistivity. Because the other variables are equal between the two resistors, we can determine that if R1:R2 is a 1:2 ratio, then ρ1: ρ2 is also a 1:2 ratio.

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