Error and Uncertainty Flashcards
What are the rules for combining uncertainties?
When adding values, add absolute uncertainties
When multiplying values, add % uncertainties
When raising values to a power, multiply % uncertainties by the power
How can you reduce the effects of random error?
Make multiple readings and take an average
How can you reduce the likelihood of systematic error?
Calibrate to avoid zero error
What is the difference between a measurement and a reading?
A reading only requires one value - a measurement requires the reading of values at both ends
The error for each reading must be accounted for when calculating the error of a measurement
Give the format for absolute uncertainties, and state the three ways of finding them
48.0 ± 0.5 kg
Either:
- half the smallest division on the instrument
- half of the last significant figure recorded
- half the range of your repeats
Give the format for % uncertainties, and state how to find them
48 ± 1 %
Divide the absolute uncertainty by the average measurement and multiply by 100
How exactly should absolute and % uncertainties be give?
% uncertainties - 1 or 2 significant figures
Absolute uncertainties - same precision as value (eg: if value is 1.22, and uncertainty is ± 0.023, round to ± 0.02)
How precisely should a value be given, compared to absolute uncertainty?
To the same precision as the absolute uncertainty (eg: if uncertainty is 0.05, and value is 3.578, round to 3.58)
How could you identify systematic error from a graph?
If a line through the origin is expected, but the line of best fit does not go through the origin, despite close correlation, this is indicative of systematic error
How could you identify random error from a graph?
If results are not closely grouped together around the line of best fit, this is indicative of random error
