BRAINCAKEMeasurements and Errors
Revision notes for Measurements and Errors in AQA Physics (7407). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- SI Base UnitsEvery physical quantity is a number multiplied by a unit.
- Derived UnitsA derived unit is made by combining SI base units, using the equation that defines the quantity.
- PrefixesPhysics deals with very large and very small values, so SI units are used with prefixes that multiply the unit by a power of ten.
- Converting UnitsCalculations must use consistent SI units, so you often need to convert values first.
- Random and Systematic ErrorsNo measurement is perfect.
- Precision, Repeatability and ReproducibilityPrecision describes how close repeated measurements of the same quantity are to each other.
- Resolution and AccuracyResolution is the smallest change in the quantity being measured that gives a perceptible change in the reading of an instrument.
- Absolute, Fractional and Percentage UncertaintyEvery measurement has an uncertainty: the interval within which the true value is expected to lie.
- Combining UncertaintiesWhen a result is calculated from several measured quantities, their uncertainties combine.
- Uncertainties on GraphsUncertainties in plotted data are shown on a graph with error bars.
- Uncertainty in a GradientWhen a gradient (or intercept) gives a physical quantity, you need its uncertainty.
- Estimation and Orders of MagnitudeThe order of magnitude of a quantity is its size given to the nearest power of ten.