What is a systematic (zero) error?
The measurements all differ from the true value by a consistent amount
What can cause a systematic (zero) error? (2)
The way in which a measurement is taken
Faulty measuring devices (wrongly calibrated, etc.)
What is a random error?
Measurement errors in which the measurements vary unpredictably
What can cause a random error? (2)
Factors that are not controlled in the experiment
Difficulty in deciding the reading given by the measuring device
What is the difference between accuracy and precision? (2)
Accuracy is to do with how close a measurement result is to the true value - closer values are more accurate
Precision is to do with how close repeated measurements are to each other - closer values are more precise
What is the uncertainty of a measurement?
An interval within which the true value is expected to lie
What is absolute uncertainty?
The +/- value after a measurement as a result of the resolution used or the range of values obtained
How is percentage error calculated?
% uncertainty = absolute uncertainty / value x 100
What is the resolution of a measuring instrument?
The smallest change in the measured quantity the instrument can show; e.g. 2 decimal places = +/- 0.01
How are errors combined when multiplying or dividing quantities?
Add percentage errors
How should a line of best fit be drawn? (2)
It should cross through all of the error bars
It should have an even number of points above and below
What is a line of worst fit?
The least acceptable straight line through the data points (steepest or shallowest)
What is the absolute uncertainty of a gradient and how is it calculated?
The positive difference between the gradient of the line of best fit and the gradient of the line of worst fit
best gradient - worst gradient |
How is the percentage uncertainty of a gradient calculated?
% uncertainty = absolute uncertainty / best fit gradient x 100
How is percentage difference calculated?
% difference = (calculated value - true value) / true value x 100
How is the maximum value calculated?
Measured value + absolute uncertainty
How is the minimum value calculated?
Measured quantity - absolute uncertainty
