BRAINCAKEMeasurements and Uncertainties
Revision notes for Measurements and Uncertainties in OCR Physics A (H156). 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.
- Random and Systematic ErrorsNo measurement is perfect.
- Precision and AccuracyPrecision describes how close repeated measurements are to each other.
- Absolute and Percentage UncertaintyA measurement is written as a value with an uncertainty, for example a wire diameter of 0.38 ± 0.01 mm.
- Combining UncertaintiesResults are usually calculated from more than one measurement, so their uncertainties must be combined.
- Uncertainties from Repeated ReadingsRepeating a measurement several times reduces the effect of random errors and helps you spot anomalous readings.
- Plotting GraphsA well-drawn graph makes patterns clear and lets you find gradients and intercepts accurately.
- Error BarsError bars show the uncertainty in plotted values.
- Best-fit and Worst-fit LinesOnce points and error bars are plotted, two straight lines are drawn.
- Uncertainty in a Gradient and InterceptWhen a gradient or y-intercept gives a physical quantity, the best-fit and worst-fit lines give its uncertainty.
- Straight-line Graphs y = mx + cA straight-line graph has the equation y = mx + c where m is the gradient (Δy ÷ Δx) and c is the y-intercept (the value of y when x = 0).
- Logarithmic GraphsLogarithms turn power-law and exponential relationships into straight-line graphs of the form y = mx + c.
- Estimating Physical QuantitiesPhysicists often need a quick estimate of a quantity: an approximate value found using sensible, rounded values, usually to one significant figure.