1.1 Measurements and their errors Flashcards
What is a random error?
An error that affects precision and
cannot be completely removed, it causes
differences in measurements.
What is a systematic error?
An error that affects accuracy and occurs
due to faults in equipment or
experimental method, causing the result
to be too large / small by the same
amount each time
What are 3 ways to reduce random
error?
● Take at least 3 repeats and calculate a
mean.
● Use a computer or a data logger.
● Use higher resolution equipment.
State a cause of parallax error
Reading a scale at a different angle each
time, to correct this you should read
scales at eye level to reduce parallax
error.
How can systematic error be reduced?
Calibrate apparatus before using e.g.
zero the balance when it is empty.
What is precision?
Precise measurements are consistent,
they fluctuate slightly about a mean
value - this doesn’t indicate the value is
accurate.
What is repeatability?
If the original experimenter can redo the
experiment with the same equipment
and method then get the same results it
is repeatable.
What is meant by resolution?
The smallest change in the quantity
being measured that gives a
recognisable change in reading.
What is meant if a value is accurate?
If the value is close to the true value.
What is absolute uncertainty?
Uncertainty given as a fixed quantity e.g.
7 +/- 0.6 V
How can percentage and fractional uncertainty be
reduced?
Measure larger quantities e.g. a longer
rope will have a smaller percentage
uncertainty than a shorter one.
What is the difference between a reading and a
measurement?
Readings are when one value is found,
measurements are when the difference
between 2 readings is found
What is the uncertainty of a thermometer
whose smallest division is 5℃?
The uncertainty in a reading is ± half the
smallest division, so the uncertainty is
± 5/2 or ± 2.5 ℃
How do you find the uncertainty in the
gradient of a line of best fit?
Draw a steepest or shallowest line of worst fit, it
must go through all the error bars.
Calculate the gradient of the best and worst line,
the uncertainty is the difference between the best
and worst gradients.
Uncertainty on graphs
● Draw a steepest and shallowest line of worst fit, it must go through all the error bars.
● Calculate the gradient of the line of best and worst fit, the uncertainty is the difference
between the best and worst gradients.
