Uncertainties

• Types of errors

  • systematic error
  • random error
• Systematic Error


  causes the same uncertainty on experimental results and will affect the accuracy of results
• Random Error

  causes different uncertainties on the experimental results
• Random error affects...

  BOTH accuracy and precision of results
• example of each type of error

  Systematic - zero error

  Random - Parallax
• Why reduce errors?

  reduces absolute uncertainty
• How to reduce systematic error?

  change experimental technique e.g reset voltmeter or ensuring balance is flat
• How does a systematic error impact results?

  changes the intercepts of the graph
• How to reduce random error?

  carry out repeats until results are concordant AND remove anomalies, calculate mean
• How do random errors impact results?

  changes intercept AND gradients of the graph, making line of best fit harder to plot
• When asked to calculate uncertainty which type must you assume?

  Absolute uncertainty
• How do you reduce percentage uncertainty?


  use a measuring device with greater resolution and use larger values for experimental results
• the uncertainty in a reading when using a particular instrument


  1/2 the resolution
• the uncertainty in a measurement

  the resolution
• Absolute Uncertainty


  val + n (unit)
• Percentage Uncertainty 


  val ± n %
• for repeated measurements


  mean value + ( range / 2 )
• % uncertainty in measurement

  absolute / value x 100
• % uncertainty in repeated measurement

  absolute / mean value x 100
• when quantities in equation are added or subtracted...

  ADD absolute uncertainties
• when quantities in equation are multiplied or divided

  ADD percentage uncertainty
• when quantities in equation contain a power...

  MULTIPLY percentage uncertainty by power value
• % uncertainty using error bars

  difference in best and worst gradient / best gradient x 100
• Percentage uncertainty in value range

  1/2 range / mean