Practical Skills: Written Assessment

• A method limitation is any experimental design flaw or fault in the method that affects the accuracy of the results
• Accuracy is how close a reading/measurement is to its true value
• Precision - how similar repeat readings/measurements are to each other
• The precision of a measurement is reflected in the values recorded – measurements to a greater number of decimal places are said to be more precise than those to a whole number
• Experiments are repeated many times to ensure the reliability of results
• The other variables in the experiment are identified and controlled in order to ensure the validity of an experiment
• Units of measurement

  A) m

  B) 1000

  C) volume

  D) decimetre

  E) area

  F) kg

  G) tonne

  
• Units of measurement

  A) s

  B) 60

  C) hour

  D) pascal

  E) 1000

  F) energy

  G) J

  H) 1000

  I) temperature

  
• • cm3 is the same as millilitre (ml)
  • dm3 is the same as litre (l)
• To reduce random error:

  Repeat measurements several times and calculate an average from them
• percentage error = (uncertainty value ÷ your measurement) x 100
• Smaller measuring instruments have higher resolution scales due to the smaller graduations on the scale. This means they have smaller margins of error
• • A small standard deviation indicates that the results lie close to the mean (less variation)
  • Large standard deviation indicates that the results are more spread out
• For qualitative and discrete data, bar charts or pie charts are most suitable
• For continuous data, line graphs or scatter graphs are most suitable

  • Scatter graphs are especially useful for showing how two variables are correlated (related to one another)
• The data should be plotted with the independent variable on the x-axis and the dependent variable on the y-axis