A measurement has a combined standard uncertainty equal to per cent of its result
PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Uncertainty in measurement · Records, communication and the epistemology of evidence
Measurement and Method, Ch Models, idealisation and what a measurement is evidence for
Problem
A measurement has a combined standard uncertainty uc equal to 0.30 per cent of its result. Four idealisations in its model equation have been priced as fractional effects on the result: effect A, +0.12 per cent; effect B, −0.05 per cent; effect C, +0.02 per cent; and effect D, known only as a bound of ±0.04 per cent, with no sign and nothing favouring any value inside it.
((a)) Find the shift in z if A, B and C were all left uncorrected and taken with the same sign.
((b)) Correct from the largest down until what remains, taken with one sign, would move z by less than about a fifth. Decide which of A, B and C to correct and which to dismiss in writing, giving the remaining Δz at each step.
((c)) Say how D enters the result, and give its standard uncertainty in per cent.