Intelligent assessment and revision tools for OCR A Physics

In a lab to determine the resistivity of a metal wire, a student measures: length L = 1.000 m with a metre rule (±1 mm), resistance R from a V–I graph (current kept low; about 3% uncertainty in the slope), and diameter d with a micrometer (±0.01 mm on a wire of about 0.50 mm, giving about 2% for d). They can make one change to most reduce the percentage uncertainty in the final resistivity. Which option should they choose, and why?

• A Replace the metre rule (±1 mm) with one of ±0.5 mm; keep everything else the same.
• B Take four times as many independent diameter readings at different positions/orientations and average them, roughly halving the percentage uncertainty in d.
• C Extend the V–I range and take many more points so the percentage uncertainty in R is reduced from about 3% to about 1.5%.
• D Double the measured length to 2.000 m using the same ruler, leaving the V–I and diameter measurements unchanged.