Physics: Uncertainties and Errors

This applies to both AS and A Level exams. You can find more examples in Appendix 10 in the Edexcel specification.

A10i Comparing results:

• Validity: a measurement is valid if it measures what it's supposed to be measuring and if the measurement taken is only affected by one independent variable
• True value: this is the value that should've been obtained if there were no experimental flaws or sources of error
• Accuracy: a result is accurate if it is close to the true value - i.e. not influenced by random and systematic errors
• Precision: how close together values from multiple repeats are
• Repeatability: how similar results are when determined by different people with the same method
• Reproducibility: how similar results are when determined by different people using a different method/different apparatus

A10ii Uncertainties and errors:

• Uncertainty: the interval that the true value should lie in with a high level of confidence. Every measurement will have an uncertainty, e.g. $\pm 0.5$$\pm 0.5$ $\mathrm{g}$$\mathrm{g}$
- Absolute uncertainty is the 'plus or minus' value
- Percentage uncertainty is the maximum percentage that the reading could be out by
percentage uncertainty $=$$=$ $\frac{\mathrm{absolute\ uncertainty}}{\mathrm{measurement}}$$\frac{\mathrm{absolute\ uncertainty}}{\mathrm{measurement}}$ $\times 100$$\times 100$
• Error: the difference between the measurement result and the true value
- Random errors are caused by unpredictable variation in the method or equipment
- Systematic errors are caused by incorrectly calibrated equipment or an incorrect technique which is used throughout
• Resolution: the smallest measuring interval in a reading (e.g. a ruler measurement would have a resolution of $1\ \mathrm{mm}$$1\ \mathrm{mm}$)