Uncertanties Flashcards
Define the term ‘scale reading uncertainty’.
Gives an indication of how precisely a scale on a measuring instrument can be read. It depends on the type of scale used – analogue or digital.
Write down the rule for finding the reading uncertainty in an analogue scale.
Reading uncertainty = ± 1/2 of the smallest scale division
Write down the rule for finding the reading uncertainty in a digital scale.
Reading uncertainty = ± 1 of the least significant digit
Define the term ‘mean’.
The best estimate of the ‘true’ value of the quantity being measured.
Write down the equation used to calculate the mean of a set of repeated measurements.
Sum of measurements/number of measurements
Define the term ‘random uncertainty’.
Arises when measurements are repeated and slight variations occur. Random uncertainty may be reduced by increasing the number of repeated measurements.
Random uncertainty may be reduced by ____________ the number of repeated measurements.
Increasing
Write down the equation used to calculate random uncertainty.
Max Value-Min Value/Number of Readings
Define the term ‘systematic uncertainty’.
Occurs when readings taken are either all too small or all too large. This can arise due to faulty measurement techniques or experimental design.
Describe a situation which could lead to a systematic uncertainty in a measurement.
Faulty measuring instrument/poor design of an experiment/failure to zero or calibrate an instrument correctly/experimenter making the same mistake each time
A graph shows a directly proportional relationship between two variables. Sketch a different graph to show how the original graph would look if there was a systematic uncertainty in the measurements for one of the variables. No numerical values are required on the axes.
Describe how you would write a measurement and its uncertainty in absolute form.
Measurement ± uncertainty (or in brackets with unit appearing after)
When we want to compare uncertainties, which form of uncertainty should we use?
Percentage uncertainties
Describe how to calculate percentage uncertainty when given a reading in absolute form (measurement ± uncertainty).
(Uncertainty/final value)x100
Write down the rule for determining the overall uncertainty in a final result.
Choose the largest percentage uncertainty.
