The number of significant figures in your final answer should match the precision of your data
Measurements & Uncertainties - OCR A-Level Physics
- The number of significant figures in your final answer should match the precisionHow close repeated measurements are to each other. A precise set of results has a small spread (low random error). of your data.
- Your result should not have more significant figures than the least precise measurement used.
- The uncertainty determines how many s.f. are meaningful.
- Example: if your answer is 9.81 +/- 0.05 m s^-2, reporting 9.8134 is meaningless -- the 4th and 5th digits are uncertain.
- Round the uncertainty to 1 significant figure, then round the result to match.
- Example: 3.456 +/- 0.073 becomes 3.46 +/- 0.07.
Common Mistake
MEDIUM
Wrong: Giving a final answer to 6 significant figures from a calculator display when the data only justified 2 or 3.
Right: Always check the significant figures of your input data. If you measured a length to 2 s.f. (e.g. 0.45 m), your final answer cannot be more precise than 2 s.f.
Right: Always check the significant figures of your input data. If you measured a length to 2 s.f. (e.g. 0.45 m), your final answer cannot be more precise than 2 s.f.
Examiner Tips and Tricks
- In practical papers and Section B calculations, you will lose marks for giving too many or too few significant figures.
- A safe rule: give your answer to the same number of s.f. as the data in the question (usually 2 or 3 s.f.).