Repeat Readings (Edexcel International A Level Physics)
Revision Note
Repeat Readings
Experiments commonly require repeat readings
This improves the accuracy of a measurement, that is dependent on the quality of the measuring instruments used to determine it, as well as the skill of the scientists involved
Repeat readings also means the data is considered reliable
The spread of the readings should be as small as possible to be precise
This ensures the measurements are not just by luck or random
Repeat readings also allows you to identify any anomalous results
This is a result that doesn't fit in with the pattern of readings
It is appropriate to have repeat readings where possible in an experiment, and to leave sufficient space in data tables to accommodate these
The average value of that variable should always be found from the repeat readings to use in further calculations
A table of results with space for repeat readings
It may not be best to repeat readings every time for all experiments
This should be decided on how easy it is to take the readings in the first place
For example, electrical components heat up from current after a while which could affect the results
Therefore, for each reading the components should be disconnected from the power supply to cool down
When they are reconnected again, the whole experiment needs to be repeated to get the repeat reading. This could take too long, especially for a wide range for the independent variable
There could also be difficulty getting repeat readings for a time dependent variable
This is because time will pass between the readings
For example, if you want to measure a dependent variable at certain time of day (e.g., between 6am-7am), the whole experiment will have to be repeated the following day, and the next and so on, which may not be in the scope of the time allowed for the experiment
Worked Example
A student is asked to determine the power of another student who runs up some stairs.
Comment on whether repeat readings are appropriate in this case.
Answer:
The student may become tired so their speed could change as they lose energy
The experiment will have to be repeated after rest, after their heart rate gets back to a regular level
The height of the stairs should be measured before each reading to check whether it stays the same
There could be difficulty of starting and stopping the stopwatch to measure the time because of reaction time
Examiner Tips and Tricks
When asked to discuss repeat readings, think about how easy it would be to take those repeat readings (commonly between 3-5 times). If it is just connecting up a circuit, or letting a pendulum oscillate, this could be quite simple. If there are possible changes that could happen to the apparatus or environment of the experiment between taking these repeat readings, then taking repeats straight away would not make it a fair test, therefore it could be best not to do so.
Remember that you will always need to take a wide range of readings (between 5-10) and experiments will have to be completed in a certain amount of time. If each reading takes 1 minute, and you are taking 10 readings, if these are all repeated 3 times this could make the experiment 30 minutes long, compared to 10 minutes!
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