Number of Readings
- When recording data from an experiment, it is important to take a suitable number of readings
- Repeat readings should also be taken where possible
- An example of a table of results with an appropriate number of readings is:
Example Table of Results with a good number of readings
- A good number of repeats is between 3 - 5 times
- In the diagram, there are 3 repeats of each reading
- Multiple measurements increase precision
- It also makes your measurements more reliable
- They also increase confidence in the experimental data
- Making the same measurement multiple times then taking an average decreases the uncertainty in the value
- The absolute uncertainty in repeat readings is equal to ± half the range of readings
- It also checks how reproducible the measurements are, so the results are not just from luck or a fluke
- Results should be recorded to the resolution of the measuring instrument which means there will be a consistent number of decimal places for the readings for any one variable
- They should be recorded to a consistent number of significant figures, which is usually 3, as this is what we can usually confidently plot on a graph
- For example, readings for a micrometer should be to two decimal places (since its resolution is 0.01 mm) whilst for a ruler, only 1 decimal place would be enough when measuring in cm, or 2 decimal places when measuring in metres (since its resolution 0.1 cm / 0.01 m / 1 mm)
Exam Tip
A common mistake when planning out experiment is not stating exactly how many readings you would take. Just saying 'take readings of the voltage' is not enough. It is better to say 'take 10 readings of the voltage, between a range of 0.5 V to 5 V in steps of 10, each with three repeats and a mean calculated'. Be as descriptive as possible to gain full marks!
