Uncertainties (Edexcel International A Level Physics)

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Uncertainities

  • Uncertainties can be represented in a number of ways:
    • Absolute Uncertainty: where uncertainty is given as a fixed quantity
    • Fractional Uncertainty: where uncertainty is given as a fraction of the measurement
    • Percentage Uncertainty: where uncertainty is given as a percentage of the measurement
  • Percentage uncertainty is defined by the equation:

Percentage uncertainty = fraction numerator u n c e r t a i n t y over denominator m e a s u r e d space v a l u e end fraction× 100 %

  • To find uncertainties in different situations:
  • The uncertainty in a reading: ± half the smallest division
  • The uncertainty in a measurement: at least ±1 smallest division
  • The uncertainty in repeated data: half the range i.e. ± ½ (largest - smallest value)
  • The uncertainty in digital readings: ± the last significant digit unless otherwise quoted

Calculating Uncertainties, downloadable AS & A Level Physics revision notes

How to calculate absolute, fractional and percentage uncertainty

 

  • Always make sure your absolute or percentage uncertainty is, at a maximum, to the same number of significant figures as the reading
  • Absolute uncertainties are compounded when adding or subtracting data 

Adding / Subtracting Data

  • Add together the absolute uncertainties

Combining Uncertainties (1), downloadable AS & A Level Physics revision notes

Examiner Tip

Remember:

  • Absolute uncertainties have the same units as the quantity
  • The uncertainty in numbers and constants, such as π, is taken to be zero

In Edexcel International A level, the uncertainty should be stated to at least one few significant figures than the data but no more than the significant figures of the data.

For example, the uncertainty of a value of 12.0 which is calculated to be 1.204 can be stated as 12.0 ± 1.2 or 12.0 ± 1.20.

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.