Module 2 - 2.2.1 Measurements and Uncertainties

Question 1

Random Errors

Answer 1

Caused by unknown and unpredictable changes during the experiment
e.g. changes in instrument/environmental conditions
e.g. human errors

Question 2

Systematic Errors

Answer 2

Introduced by an inaccuracy in the apparatus or its use
Errors are present in all values and can be removed once identified
e.g. zero errors

Question 3

Accuracy

Answer 3

The degree to which a value obtained by an experiment is close to the true value

Question 4

Precision

Answer 4

The degree to which repeated values collected under the same conditions in an experiment show the same results
- the smaller the range of repeated values, the higher the precision
(not affected by systematic errors)

Question 5

Resolution

Answer 5

The smallest change in a quantity that an instrument can measure

Question 6

Absolute Uncertainties

Answer 6

The smallest division on the measuring instrument used
(for a stop watch use reaction time)

Question 7

Percentage Uncertainty

Answer 7

absolute uncertainty/measured value x100%

Question 8

When multiplying variables

Answer 8

Add the percentage uncertainties together

Question 9

How to Read a Micrometer

Answer 9

• place the object between the jaw of the micrometre
• the horizontal scale is called the barrel scale
• this gives a reading of millimetres and half millimetres
• the vertical scale is called the thimble scale
• read the barrel scale by looking at the edge of the thimble
• • top row of axis = mm
• • bottom row of axis = half mm
• • e.g. gives 14.5mm
• find where the thimble scale lines up exactly with the barrel scale axis
• • each mark represents 0.01mm
• • e.g. if read 33, add 0.33 to previous reading
• overall gives 14.83mm