Precision & Accuracy (Edexcel International A Level Physics)

Precision

• Precision is how close the measured values are to each other
• If a measurement is repeated several times, then they 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 to a greater number of decimal places are said to be more precise than those to a whole number

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 an estimate of the difference between a measurement reading and the true value
• 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
• In other words, this is the smallest change the instrument can detect

• This is slightly different to resolution
• Resolution is the smallest change the instrument can observe but sensitivity is the smallest change that the instrument can detect
• 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 sensitivity detects changes in a variable much better
  • For example, a thermometer could have a sensitivity of 1 °C (it only detects change of 1 °C)
  • A digital thermometer could have a sensitivity 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 give much more accurate results