2.2 making measurements & Analysing Data Flashcards
what is accuracy?
how close a value is to the commonly accepted value or TRUE VALUE
what is precision?
relates to how close together repeat values are, smaller the range = more precise
what is a systematic error?
this includes (zero errors), these are errors that are the same every time you repeat the experiment, (they shift the values by the same amount), usually due to incorrect calibration of equipment, they affect the accuracy but not the precision of your results
what is a random error?
an error caused by unknown and unpredictable changes during an experiment, can be caused by changes in instruments or in the environment (e.g fluctuations in temperature), they affect both precision and accuracy
what is a human error?
a one-off mistake, an anomalous result caused by human mistakes that can be removed
what is an uncertainty?
an error in a piece of measuring equipment which could change measurements (e.g due to a lack of sensitivity)
what is the absolute uncertainty for single readings?
+- the resolution, the smallest division on the measuring equipment used (the smallest change it can read)
what is the absolute uncertainty for several/a group of readings?
0.5 x the range, or half the spread to find absolute uncertainty
what is the formula for percentage uncertainty for single readings?
absolute uncertainty/measured value x 100
what is the formula for percentage uncertainty for a group of readings?
absolute uncertainty/mean of values x 100
remember here the absolute uncertainty = 0.5 x range
when combining percentage uncertainties, what is the rule?
percentage uncertainty of a + percentage uncertainty of b
y=a+/-b
when combining percentage uncertainties, what is the rule?
percentage uncertainty of a x n
how do you represent uncertainty of individual values on graphs?
plot error bars on each point (shows the range where the true value is likely to lie in)
how you work out the percentage uncertainty of a gradient of a line or the y-intercept of a line?
first plot all points and add error bars to each points
draw a line of best fit through as many of the points as you can (ensure it passes through all the error bars)
calculate the gradient of the LOBF
then draw a line of maximum gradient and minimum gradient (lines of worst fit that still go through all the error bars)
absolute uncertainty = 0.5 x (max gradient - min gradient) OR (best gradient - one of the worst gradient)
percentage uncertainty = absolute uncertainty/gradient of LOBF x 100
what is a zero error?
when the apparatus or equipment shows a non-zero value when it should be registering a value at exactly zero
