Anomalous Readings (Edexcel IAL Physics)

Anomalous Readings

• Experimental errors (also known as operator errors or ‘one off’ errors) will affect the results of an experiment and can produce anomalies

  • These anomalies should be identified during the evaluation of results and before drawing conclusions

• Anomalies can be identified by looking for results or data points on a graph that do not fit with the trend or with other repeat readings carried out during the experiment

  • These anomalous results will show a larger difference from the mean than the rest of the results (a result is often taken to be anomalous if it differs from the mean result by more than 10%)

• The results or ‘data’ collected from an experiment can be made more reliable if the experiment is repeated several times and anomalies are removed

  • This, in turn, allows more valid conclusions to be drawn

• Anomalous results are always inconsistent with other readings e.g., a point that is not on the line of best fit of a graph

Identifying an anomalous result from a graph

• If an anomaly occurs in the experiment:

  • Ignore this value when calculating the mean
  • Repeat this measurement

Worked Example A student achieves a set of repeat readings for the current through a bulb.

2.5 mA	2.8 mA	6.1 mA	2.0 mA	2.3 mA

Calculate the mean current through the bulb.

Answer:

Step 1: Identify the anomalous result

• The only result that doesn't fit with the rest of the data is 6.1 mA
• This can be ignored when calculating the mean

Step 2: Calculate the mean current

Mean current = $\frac{2.5+2.8+2.0+2.3}{4}$ = 2.4 mA

Exam Hint When calculating the mean of some repeat readings for data given in your practical paper, always ignore any anomalous readings that are inconsistent when calculating the mean.