Uncertainty calculator for A-level Physics
Uncertainty in a product, quotient or power
113 ± 4
Questions people ask
How do you calculate percentage uncertainty?
Divide the absolute uncertainty by the value and multiply by 100. For (6.0 ± 0.1) cm that is 0.1 ÷ 6.0 × 100 = 1.7%.
What happens to uncertainty when you square a value?
Its percentage uncertainty doubles. A power multiplies the percentage uncertainty by the size of the power.
What is the uncertainty from repeat readings?
Half the range. Readings of 1.23, 1.32, 1.27 and 1.22 m have a range of 0.10 m, so the uncertainty is ±0.05 m (AQA practical handbook).
Do uncertainties subtract when you subtract values?
No. Absolute uncertainties add for both sums and differences.
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How we work this out
What it does
Enter repeat readings, or values with their uncertainties: get the absolute and percentage uncertainty, worked by AQA's rules.
The uncertainty calculations in AQA A-level Physics (7408) section 3.1.2 and the practical handbook: repeat readings, sums and differences, products, quotients and powers.
Method
- Repeat readings: the value is the mean and the uncertainty is half the range (AQA practical handbook).
- Sums and differences: absolute uncertainties add.
- Products and quotients: percentage uncertainties add. A power multiplies that quantity's percentage uncertainty by the size of the power. A constant such as π adds nothing.
- The answer is quoted with the uncertainty to 1 significant figure and the value to the same decimal place.