Uncertainties Flashcards
Define accuracy
How close to the true value your measurements are
Define precision
How close your measurements are to each other.
What factors can affect the confidence in accuracy and precision of measurements made
Scale of measurement instrument (scale reading uncertinty)
Ability of person to make the measurement (Random uncertainty)
How do you tell the scale reading uncertainty on a digital scale.
For digital scales the uncertainty is +/- the smallest digit displayed.
How do you tell the scale reading uncertainty on an analogue scale
For analogue scales the uncertainty is +/- one half of the smallest division.
When do random uncertainties occur
Random uncertainties occur in measurements that involve:
Human reaction time (ie timing a falling object)
Rapid fluctuations (ie measuring air speed)
How can random uncertainties be reduced
Repeating measurements and then finding the mean (average) of the repeated measurements
How do you calculate random uncertainty in the mean
(Max reading - Min reading)/ number of readings
What is an absolute uncertainty
If an uncertainty is expressed in the same units as the measurement it is called the absolute uncertainty
What is a percentage uncertainty
If an uncertainty is expressed as a percentage of the measured value it is called the percentage uncertainty.
Why are percentage uncertainties used
they are easier to compare
How do you calculate a % uncertainty
% uncertainty = (absolute uncertainty/ mean measurement) x 100%
If multiple measurements with different uncertainties are combined in a calculation which uncertainty is used
The biggest percentage uncertainty in any single measurement will be the uncertainty in the final calculated value.
Describe a systematic uncertainty
A systematic uncertainty affects all measurements by the same amount.
How are systematic uncertainties usually identified.
Usually identified from a graph of experiemntal results. every value on an axis will be off by the same amount.
