The resistance of a uniform wire is
Correct answer: B. proportional to its length and inversely proportional to its cross sectional area
- A. proportional to its length and to its cross sectional area
- B. proportional to its length and inversely proportional to its cross sectional area
- C. independent of its dimensions
- D. inversely proportional to its length
Explanation
R equals rho L over A, so a longer wire offers more resistance and a thicker one less, which is why thick cables are used for heavy currents. The constant rho is the resistivity, a property of the material rather than of the sample. Doubling the diameter quarters the resistance, because area depends on the square of the radius.
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About Resistance and Resistivity
Resistance measures opposition to current in a conductor and follows R = V/I for an ohmic conductor, while resistivity is an intrinsic property of the material. Questions use R = ρL/A, examine effects of length, cross-sectional area and temperature, and distinguish resistance, resistivity, conductance and conductivity.
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