1. Teacher’s Notes
This sequence of slides is designed to introduce, and explain the taking of measurements, including the meaning of variation, range, mean (average) and the difference between accuracy & precision, as explained on page 362 in New Physics for You, 2006 edition.
On each slide the key points are revealed step by step, at the click of your mouse (or the press of a key such as the space-bar).
Before making the next mouse-click you can ask questions of the class or make statements about what is about to be revealed.
This should help students to become clearer about the ideas involved.
Naturally it pays to have quick practice-run first.
To start the slide-show, press function-key F5 (or right-click->Full Screen) (to return to ‘normal view’ press the <Esc> key).
For more free PowerPoint presentations, visit

2. New Physics for You, page 362
How Science works:
Taking measurements
New Physics for You, page 362

3. Learning Objectives
You should learn :
About taking measurements,
The meaning of ‘variation’, ‘range’ and ‘mean (average)’,
The meaning of ‘accuracy’ and ‘precision’.

4. Taking measurements When you take measurements
there may be some variation in the readings.
For example:
If you time the fall of a paper parachute over a fixed distance, the times may vary slightly.
10.1 s, s, s, s, s
Let’s look at these results more closely.

5. Taking measurements The results were:
10.1 s, s, s, s, s
What is the Range of these results?

6. Taking measurements : Range
The results were:
10.1 s, s, s, s, s
Find the minimum value
and the maximum value
Range
= max – min
= 10.3 – 9.9
= 0.4 s

7. Taking measurements : Mean
The results were:
10.1 s, s, s, s, s
What is the mean (or average) of these results?

8. = 50.5 5 Taking measurements : Mean The results were:
10.1 s, s, s, s, s
Add up the 5 numbers:
= 50.5
There are 5 items, so divide by 5:
Mean (or average) = =
= 10.1 s

9. Taking measurements : Mean
The results were:
10.1 s, s, s, s, s
Why is it a good idea to calculate the mean of your results?
Because it improves the reliability of your results.
Your results will be more reliable.

10. Accuracy
and
Precision

11. Accuracy and Precision …sound the same thing…
Definitions
Accuracy and Precision …sound the same thing…
…is there a difference??

12. Definitions : Accuracy
In your experiments, you need to consider the accuracy of your measuring instrument.
For example:
An expensive thermometer is likely to be more accurate than a cheap one.
It will give a result nearer to the true value.
It is also likely to be more sensitive. So it will respond to smaller changes in temperature.

13. Definitions : Precision
As well as accuracy, precision is also important.
Precision is connected to the smallest scale division on the measuring instrument that you are using.
For example:

14. Definitions : Precision
For example, using a ruler:
A ruler with a millimetre scale
will give greater precision than a ruler with a centimetre scale.

15. Definitions : Precision
A precise instrument also gives a consistent reading when it is used repeatedly for the same measurements.
For example:

16. Definitions : Precision
For example, 2 balances:
A beaker is weighed on A, 3 times:
The readings are: 73 g, 77 g, 71 g A
So the Range is:
= 6 g
It is then weighed on B, 3 times:
The readings are: 75 g, 73 g, 74 g
So the Range is: B
= 2 g
Balance B has better precision.
Its readings are grouped closer together.

17. Learning Outcomes
You should now understand:
The meaning of ‘variation’ and ‘range’,
How to calculate the mean (or average),
and why this improves the reliability of your results,
The difference between ‘accuracy’ and ‘precision’.

18. Summary
We calculate the average of a set of results e.g. rainful in January over 10 years as this gives us a more reliable result.
A precise rain gauge will give results in ml rather than cm.
The range of the results=
highest value – lowest value
Precise results will have a smaller range
An accurate result is nearer to the true value

19. On your own work through the exercise on the sheet

20. Answers Average Range Ammeter A 1.33 0.23 Ammeter B 1.33 0.03
Ammeter C
2. A
3. B
4. C

21. For more details, see:
New Physics for You, page 362
For more free PowerPoints, visit
the web-site at

22. If you are connected to the web at the moment, click below to see what’s available: