Testing whether contact resistance at the crocodile clips biases a resistivity measurement

PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Data analysis and model fitting in the laboratory · Designing and running experiments

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Problem

Testing whether contact resistance at the crocodile clips biases a resistivity measurement, a group repeats the wire-resistivity measurement of Chapter 5 with freshly cleaned clips. With the original clips the result was (1.680±0.030)×10−8 Ω m(1.680\pm0.030)\times10^{-8}\,\Omega\,\mathrm{m}; with cleaned clips it is (1.702±0.032)×10−8 Ω m(1.702\pm0.032)\times10^{-8}\,\Omega\,\mathrm{m}. The two runs use independent readings. Someone writes: "The shift, 0.022×10−8 Ω m0.022\times10^{-8}\,\Omega\,\mathrm{m}, is less than either uncertainty, so contact resistance has no effect on the result." ((a)) Compute the consistency ratio zz for the shift between the two clip conditions. ((b)) Find the error in the quoted conclusion, and state what should be entered in the uncertainty budget instead of "no effect."

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