Paper 3 Flashcards
Validity
Measurement measures what it is supposed to be measuring. This depends on the method and instruments.
True Value
Value which would have been obtained in an ideal measurement.
With the exception of a fundamental constant, the true value is considered unknowable.
Accuracy
Measurement close to true value.
Influenced by random and systematic errors.
Precision
Consistency between values obtained by repeated measurements.
Influenced by random effects.
Precise if values cluster closely together.
Repeatability
Similar results are obtained by students from the same group using the same method.
Precision can be used to judge this.
Reproducibility
When similar results are obtained by students from different groups, using different methods/apparatus.
Uncertainty
Interval within which the true value can be considered to lie, within a given level of confidence.
This is subject to systematic or random effects.
This can be estimated by considering the instruments and method.
Error
Difference between the measurement result and the true value, if a true value is thought to exist.
Resolution
The smallest measuring interval and the source of uncertainty in a single reading.
Significant figures
Depends on the resolution of the measuring instruments.
Uncertainties for: ruler, micrometer, vernier
Ruler: +- 1mm
Vernier: +- 0.1mm
Micrometer: +- 0.01mm
Normal human reaction time
0.2 seconds
How to measure wire diameter
Check for zero error
Check in 3 places, in case wire is not uniform
If wire has some kinks, actual length may be greater than measured length
A.ways measure stated values (eg 100g masses)
Benefit of data loggers
5 decimal places
Eliminate human uncertainty
High resolution
More frequent readings
BUT- could have systematic errors (most commonly zero error)
What to criticise
Range, always 6 readings, interval, significant figures (consistent with column and consistent with measuring device)
