Physics Practical Key Words

Key Words for Physics Edexcel Practicals

Validity

A measurement is valid if it measures what it is meant to. It depends on using the right method and instruments.

True value

The true value is the value that would have been obtained in an ideal measurement. The true value is considered unknowable – with the exception of a fundamental constant.

Accuracy

A measurement is accurate if it is close to the true value. It is influenced by random and systematic errors.

Precision

A measurement is precise if the values ‘cluster’ closely together. It is the consistency between values obtained by repeated measurement. It is only influenced by random errors.

Repeatability

A measurement is repeatable when similar results are obtained by a single operator using a single method over a short timescale.

Reproducibility

A measurement is reproducible when similar results are obtained by different operators using different methods. It is a harder test of the quality of data.

Uncertainty

Uncertainty is the range where the true value is likely to be. Any measurement will have some uncertainty; it comes from random or systematic errors and depends on the method and instruments used. It’s usually shown like this: 20 °C ± 2 °C.

Uncertainty is often half the smallest unit of the instrument. For example, with a mm ruler, the uncertainty is ±0.5 mm.

Error

Error is the difference between the measurement result and the true value (if one exists). This is not a mistake in the measurement. The error can be due to both systematic and random effects. An error of unknown size is a source of uncertainty.

Resolution

Resolution is the smallest unit an instrument can measure. It’s also the source of uncertainty in a single reading.

Significant figures

The number of SF used in recording the measurements depends on the resolution of the measuring instruments. It should be the same as the instrument with the fewest SF in its reading - the lowest precision.

Reliability

Measurements are reliable if consistant values are obtained each time the same measurement is repeated.