2.2 - Making Measurements and 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, 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, affecting 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.
What is the absolute uncertainty for single readings?
+- the resolution, the smallest division on the measuring equipment used.
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 for y=a+/-b?
Percentage uncertainty of a + percentage uncertainty of b.
When combining percentage uncertainties, what is the rule for y=ab?
Percentage uncertainty of a + percentage uncertainty of b.
When combining percentage uncertainties, what is the rule for y=a/b?
Percentage uncertainty of a + percentage uncertainty of b.
When combining percentage uncertainties, what is the rule for y=a^n?
Percentage uncertainty of a x n.
How do you represent uncertainty of individual values on graphs?
Plot error bars on each point.
How do 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 point. Calculate the gradient of the line of best fit. Then draw lines of maximum and minimum gradient. Absolute uncertainty = 0.5 x (max gradient - min 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.
Give an example of a systematic error.
Parallax errors, caused by reading a scale at a wrong angle.
