Physical Science / Unit 1: Science Skills and Measurement
1.6 Accuracy, Precision and Error
Notes
- Accuracy is how close a measurement is to the true (accepted) value.
- Precision is how close repeated measurements are to each other.
- Measurements can be precise but not accurate, for example from a scale that is not zeroed.
- Percent error $\displaystyle = \frac{|\text{measured} - \text{accepted}|}{\text{accepted}} \times 100\%$.
- Example: Measured 9.5 g, accepted 10.0 g. $\displaystyle \frac{0.5}{10.0} \times 100\% = 5\%$.
- Repeating trials and averaging reduces the effect of random error.
Practice
A scale always reads 2 g too high. Three measurements of a 50 g mass are 52 g, 52 g and 52 g. These are:
The values agree with each other (precise) but are not close to 50 g (not accurate).
A student measures the boiling point of water as 98 degrees C. The accepted value is 100 degrees C. What is the percent error?
$\displaystyle \frac{2}{100} \times 100\% = 2\%$.
Which action best improves the reliability of an experiment's results?
Repeated trials reduce the effect of random error.
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