Precision & Accuracy (Edexcel International A Level (IAL) Physics): Revision Note

Precision & Accuracy

Precision

• Precision is how close the measured values are to each other

• If a measurement is repeated several times, then it can be described as precise when the values are very similar to, or the same as, each other

• The precision of a measurement is reflected in the values recorded

  • Measurements that are more tightly grouped when repeated are said to be more precise

  • Recording to more decimal places reflects the resolution of the instrument, not the precision of the measurements

Accuracy

• Accuracy is how close a measured value is to the true value

• Accuracy can be increased by repeating measurements and finding a mean average

The difference between precise and accurate results

• Measurements of quantities are made with the aim of finding the true value of that quantity

• In reality, it is impossible to obtain the true value of any quantity, there will always be a degree of uncertainty

• The uncertainty is the interval within which the true value can be expected to lie, with a given level of confidence

• Random and systematic errors are two types of measurement errors which lead to uncertainty

Representing precision and accuracy on a graph

Sensitivity

• A measuring instrument can have a sensitivity

  • This is the ratio of the changes in the output of an instrument to the change in value of the quantity being measured

• This is slightly different to resolution

• Resolution is the smallest measuring interval the instrument can show

• If what you are measuring (the dependent variable) changes significantly when the independent variable is changed, then the instrument is deemed to be sensitive

  • If the value does not change significantly, with big changes to the independent variable, then the instrument is not sensitive

• An instrument with better resolution can show smaller changes in a variable

  • For example, a thermometer could have a resolution of 1 °C (it only shows changes of 1 °C)

  • A digital thermometer could have a resolution of 0.1 °C (it can detect changes as small as 0.1 °C)

• If you are taking measurements in very small intervals of temperature increase, the digital thermometer will be able to show much smaller changes in temperature