1.2 - Practical skills
● Precision VS accuracy
○ ***Precision/reliability: how close a set of repeated measurements are to
each other (influenced by random errors)
○ ***Accuracy: how close a measurement is to true/accepted value (influenced
by systematic + random errors)
● ***Error: how far away a value is from the true value
● Systematic VS random error
○ ***Systematic error: consistent shift in readings causing deviation
from true value, cannot be reduced by repeated measurements, eg
zero error on device, parallax error (on observations)
○ ***Random error: unpredictable variation in measurements, can be
reduced by repeated measurements (5~10 times) & calculating mean
● ***Repeatability: repeatable experiment if - same experiment, same equipment,
same result (a number of times, over short time period)
● ***Reproducibility: reproducible experiment if - same experiment, different
equipment, same quantity, similar/same result
Measurement and uncertainty
● Measurement: 2 judgements\uncertainties (including digital devices), reading: 1
judgement\uncertainty
● ***Uncertainty: range of values (±) which could reasonably contain true value of a
measurement - based on resolution of given measuring instrument + confidence an
experimenter has about their result
○ All answers to calculations should be to same no. of s.f.s given in
question/read from measuring instruments
○ If ± quantities with uncertainties, add absolute uncertainties
Eg (1.5 ± 0.1) + (7.95 ± 0.05) = 9.45 ± 0.15
1
● Precision VS accuracy
○ ***Precision/reliability: how close a set of repeated measurements are to
each other (influenced by random errors)
○ ***Accuracy: how close a measurement is to true/accepted value (influenced
by systematic + random errors)
● ***Error: how far away a value is from the true value
● Systematic VS random error
○ ***Systematic error: consistent shift in readings causing deviation
from true value, cannot be reduced by repeated measurements, eg
zero error on device, parallax error (on observations)
○ ***Random error: unpredictable variation in measurements, can be
reduced by repeated measurements (5~10 times) & calculating mean
● ***Repeatability: repeatable experiment if - same experiment, same equipment,
same result (a number of times, over short time period)
● ***Reproducibility: reproducible experiment if - same experiment, different
equipment, same quantity, similar/same result
Measurement and uncertainty
● Measurement: 2 judgements\uncertainties (including digital devices), reading: 1
judgement\uncertainty
● ***Uncertainty: range of values (±) which could reasonably contain true value of a
measurement - based on resolution of given measuring instrument + confidence an
experimenter has about their result
○ All answers to calculations should be to same no. of s.f.s given in
question/read from measuring instruments
○ If ± quantities with uncertainties, add absolute uncertainties
Eg (1.5 ± 0.1) + (7.95 ± 0.05) = 9.45 ± 0.15
1
