Edexcel A-Level Physics Combined Measurement Uncertainty

Review combined measurement uncertainty in Edexcel A-Level Physics through subtracted readings, powered terms, percentage uncertainty and range comparisons.

Exam points

add absolute uncertainties for subtracted readings before converting the result to percentage uncertainty
double a percentage uncertainty for squared terms before adding the remaining percentage uncertainties
use upper and lower limits from combined uncertainty to support a valid physical conclusion

[Maximum number: 2]

An L-shaped steel rod was held horizontally in a stand clamped by its shorter end as shown.

The end of the steel rod was at a height p above the bench. A student attached a mass m to the end of the steel rod causing it to bend towards the bench. The end of the steel rod was then at a height q above the bench.

Figure for Question C.1.5—Combined measurement uncertainty question 1 — Edexcel A-Level Physics A2

The difference between p and q was recorded as 26 mm ± 1 mm.

Explain why the uncertainty in this value is given as 1 mm.

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C.1.5—Combined measurement uncertainty question 1