Uncertainties Flashcards
scale reading uncertainity
Tells us how accurately a scale on a measuring instrument can be read.
It depends on the type of scale used—analogue or digital.
Random Uncertainty
The slight variations in readings that occur when measurements are repeated.
The more a measurement is repeated, the smaller the random uncertainty.
Systematic Uncertainty
When all measurements are affected in the same way e.g. the readings are all
too high or too low due to a faulty measuring instrument or failure to ‘zero’ an
instrument before taking readings.
Calibration Uncertainty
The difference between a manufacturer’s claim for the accuracy of an
instrument when compared with an approved standard.
Absolute Uncertainty
Expressing an uncertainty in absolute form, i.e. final value ± uncertainty.
Values should normally be rounded to one significant figure.
Percentage Uncertainty
Expressing an uncertainty in percentage form. This is useful for comparing
uncertainties.
Error Bars
Used to represent the absolute uncertainty of values on a graph.
When drawing a straight line graph, the best fit line should pass through all of
the error bar lines.
Accuracy
Describes how close a measurement is to the true or accepted value.
Precision
Describes how close a number of measurements are to one another.
Calibration uncertainty in a metre stick (wood)
0.5mm
Calibration uncertainty in ruler made of steel
0.1mm
Calibration uncertainty in digital meter
0.5% of reading + 1 of smallest division
scale reading uncertainty in analogue scale
+ or - half the smallest division
scale reading uncertainty in digital scale.
+ or - 1 of the smallest division
when combining uncertainties, when can an uncertainty be ignored?
if it is less than one third of the magnitude of the uncertainty in another measurement.
