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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.

Syllabus
Pearson Edexcel International Advanced Subsidiary/Advanced Level
Course
Physics XPH11/YPH11
Level
AS

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

C.1.5—Combined measurement uncertainty question 1

[Maximum number: 2]

A student carried out an experiment to compare the speed of sound in air and the speed of sound in wood. The student used a long piece of wood, a hammer and two microphones, as shown.

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

The microphones were connected to a 2-beam oscilloscope. The student hit the wood with a metal hammer producing a sharp sound that travelled through the air. The oscilloscope traces produced by the microphones and the time per division dial are shown.

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

The student was given the following equation and data to find a value for the speed of sound in oak.

v = √(E/ρ)

Young modulus E of oak = 11.2 GPa ± 0.5 GPa
Density ρ of oak = 650 kg m^-3 with an uncertainty of 3%

Assess which of these values was the more significant source of uncertainty in the value of the speed of sound.

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