Physics M1P1 - Practical skills

Systematic errors

• Something wrong with the instrument or its data handling system

• Instrument used wrongly by the student

• Zero errors, fixed by subtracting wrong amount

Random errors

• Unknown and unpredictable variation, caused by changes to instrument and environment

Anomalies

• Data points that don’t fit the pattern of the data

• Errors in reading values, mistakes

Accuracy vs Precision

Accuracy - A measure of how close a measurement is to the true value

Precision - A measure of how close your results are to each other

Resolution

Smallest increment on the scale of an instrument

* Refers to instruments, accuracy precision and uncertainty refers to data

Absolute uncertainty rounding

• 1 sig. fig

• Cannot be more precise than the measurement itself (To more d.p)

Absolute uncertainty rules

• Analogue - ± half the resolution

• Digital - ± the resolution

• Rulers - ±1mm (for rulers in mm) *includes micrometers and calipers

• Stopwatches - ±0.3s (Human reaction speed)

Uncertainty in a mean

Mean ± (Range ÷ 2)

Assumed uncertainty

± ‘1’ of the last sig fig

e.g 5.27V will have ±0.01V

Combining uncertainties (+ and -)

Final uncertainty is just all the absolute uncertainties added regardless of adding or subtracting values

Combining uncertainties (x and ÷)

Add up percentage uncertainties and convert it back in the end

Squaring uncertainties

Add the percentage uncertainty to itself (basically double it) and then convert it back in the end

Square rooting uncertainties

Half the percentage uncertainty, convert it back in the end

Uncertainty in gradients

• Absolute uncertainty = ±Difference between LOBF gradient and LOWF gradient
  

• Percentage uncertainty = (Uncertainty ÷ Gradient of LOBF) x 100 then convert it back in the end

*If you have two LOWFs (steepest and shallowest) you have to divide the difference by 2, before calculating % uncertainty.

Uncertainty in y-intercepts

• Absolute uncertainty = ±Difference between LOBF y-int. and LOWF y-int.
  

• Percentage uncertainty = (Uncertainty ÷ LOBF y-int.) x 100 then convert it back in the end

*If you have two LOWFs (steepest and shallowest) you have to divide the difference by 2, before calculating % uncertainty.

Prefixes and their multipliers