6.14 Calculations using Experimental Data

• Collecting experimental data is only some of the work required when carrying out a practical
• When setting up a data table, space must always be left for some calculations
• The most common calculation is the mean for repeat readings

Mean = 

• The value of the mean is then used in for further calculations
  
  • Anomalous readings should be ignored in this calculation
• The mean should have the same number of significant figures as the readings used to calculate it

• The experiment may require to calculate a variable which you can't directly measure
  • E.g., the area of a wire
• In this case, other measurements are taken, which then by using an equation, the variable that is required can then be calculated
  • E.g., area of a wire = πr², so r is measured for the wire using a micrometer and substituted into this equation to calculate the corresponding area for each value of r
• Another example of this is finding the 'log' of a value
  • One column in a data table should be for the measurement
  • A column next to it should be the for the 'log' of that measurement
• In the Hooke's law experiment, the 'extension' cannot be measured direction, but can be calculated from the final and initial length, which can be measured 

Hooke's Law Table of Results

• The average current is calculated by

• The resistance is calculated using the equation

• All readings are to 3 significant figures, so all values calculated should also be to 3 s.f.