Multiple choiceQuestion 1 · Recall
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By the end you can explain how random errors and systematic errors (including zero errors) affect measurements, recognise each from a description or a graph, and correct a zero error.
The error in a reading is how far it is from the true value. Errors come in two flavours, and they behave completely differently.
Random error
An error that makes repeated readings scatter unpredictably above and below the true value, by a different amount each time.
Systematic error
An error that makes every reading differ from the true value by the same amount (or the same proportion) in the same direction.
Zero error
A systematic error in which an instrument gives a non-zero reading when the true value is zero, for example a balance that reads 0.4 g with nothing on it.
| Random error | Systematic error | |
|---|---|---|
| Effect | readings scatter both ways | all readings shifted one way |
| Typical causes | reaction time on a stopwatch; judging a scale between marks; readings that fluctuate | zero error; a wrongly calibrated scale; reading a scale from the same wrong angle every time (parallax) |
| Repeat and average? | reduces it | no help at all |
| Fix | repeat readings and average; plot a graph with a best-fit line | recalibrate; correct for the zero error; improve the technique |