Measurement and Errors Flashcards
What is absolute error?
The difference between a measured value and the true value
If the absolute error is a very small number, does that mean it was an excellent experiment?
Not necessarily as the error if relative to the size of the measured values
Which has the smallest absolute error, 3.5mg or 3ms^-1?
Neither as you can’t compare because they have different units
What is the equation for percentage error?
% error = (absolute error / true value) x 100
What unit is percentage error measured in?
It has no unit
What can be said about an experiment if the percentage error is as small as possible?
The experiment was carried out well
What does an accurate result mean?
A result which is close to the true value (has a small percentage error)
What 2 types of error are there?
Random error
Systematic error
What is random error?
An error that doesn’t follow a consistent pattern
What is an example of a source of random error?
Instruments don’t have infinite resolution
What is systematic error?
An error that has a consistent pattern
What is an example of a source of systematic error?
Incorrect calibration of an instrument (e.g. a micrometre with jaws closed reads 0.02mm so every measurement is 0.02 mm greater)
What is absolute uncertainty?
The interval within which the true value is expected to lie
What can you think uncertainty as?
The ‘worst case scenario’ estimate of random error
What is the equation for percentage uncertainty?
% uncertainty = (absolute uncertainty / measured value) x 100
What is resolution?
The smallest division on the scale of an instrument
How do you estimate uncertainty using the resolution of the instrument?
If the instrument has a resolution of 0.01mm, the uncertainty will always be at least ±0.01 mm
What is the best way of estimating uncertainty?
Working out ± half the range of repeated measurements
What are 3 methods of reducing Random error?
Use a measuring device with a higher resolution
Measure a larger quantity
Repeat and average
How does using a measuring device with a higher resolution reduce Random error?
It can reduce absolute error, and therefore percentage error
How does measuring a larger quantity reduce Random error?
It will mean that the error is a smaller percentage of the measured value
How does repeating and averaging reduce Random error?
It helps to spot anomalous results (which can then be removed before averaging)
What does repeating and averaging not help with?
Reducing systematic error on final values
What can you do if you suspect systematic error?
Calibrate your apparatus by measuring a known value
What does calibration help with?
Reducing systematic error as if there’s a difference between your measurement and the known value, you can use this value to correct the inaccuracy
What is a zero systematic error?
Where an instrument will read a different value when it should be 0
How can you see if a graph is directly proportional?
If the line of best fit is a straight line that goes through the origin
What is a parallax error?
An error that occurs because of the angle of view of the observer
How can you reduce parallax error?
Adjusting the field of view so that the line of sight is perpendicular to the plane of the scale
What is the ‘pin and mirror’ technique?
A mirror can be used to ensure that the line of sight is perpendicular to the scale
What are anomalous results?
Results that do not fit the pattern of the rest of the data
When adding or subtracting values (with the same units), what do you do with the absolute errors?
Add them
When multiplying or dividing values (with the same units), what do you do with the percentage errors?
Add them
When raising a power to the power of n, what do you do to the percentage error?
Multiply by n
