A notebook entry for a length of aluminium wire reads: Diameter: mean of ten…
PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Quantities, units and the practice of measurement · Quantities, units and the practice of measurement
Measurement and Method, Ch What a measured value is: quantities, units and the SI
Problem
A notebook entry for a length of aluminium wire reads: Diameter: mean of ten micrometer readings at stations spaced evenly between two marked points, 0.500mm. Two-lead reading across the whole 1.000m piece: 0.39Ω. Four-terminal reading, current fed through the ends of the piece, voltage sensed between the two marked points, which are 0.8000m apart: 0.1080Ω. Relative uncertainty of the resistivity, supplied by the demonstrator: 2.3%. The result written under it is ρ=2.12×10−8Ωm.
((a)) Say which resistance and which length belong to the measurand "the resistivity of the wire between the two marked points", and find the mistake in the entry.
((b)) Compute ρ correctly, treating the wire between the marks as a uniform cylinder of the mean diameter.
((c)) Write the result in the house form and in the concise bracket notation.
((d)) Name one further piece of information the entry needs before another laboratory could use the result.