2. Teacher’s Notes This sequence of slides is designed to introduce, and explain, the idea of errors in practical work, as explained on pages 8 and 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 key). For more free PowerPoint presentations, visit www.physics4u.co.uk

3. How Science works: Errors New Physics for You, pages 8, 362

4. About different types of errors, How to reduce them when you are doing your practical work. Learning Objectives You should learn :

5. What is an error? An error is a mistake of some kind... …causing an error in your results… …so the result is not accurate.

6. What is an error? Some are due to human error… For example, by not using the equipment correctly Let’s look at some examples.

7. Human error Example 1 Professor Messer is trying to measure the length of a piece of wood: Discuss what he is doing wrong. How many mistakes can you find? Six?

8. Human error 1. Measuring from 100 end 2. 95.4 is the wrong number 3. ‘mm’ is wrong unit (cm) 4. Hand-held object, wobbling 5. Gap between object & the rule 6. End of object not at the end of the rule 7. Eye is not at the end of the object (parallax) 8. He is on wrong side of the rule to see scale. Answers: How many did you find?

9. Human error Example 2 Reading a scale: Discuss the best position to put your eye. your eye

10. Human error 2 is best. 1 and 3 give the wrong readings. This is called a parallax error. your eye It is due to the gap here, between the pointer and the scale. Should the gap be wide or narrow?

11. Anomalous results When you are doing your practical work, you may get an odd or inconsistent or ‘anomalous’ reading. This may be due to a simple mistake in reading a scale. The best way to identify an anomalous result is to draw a graph. For example...

12. Anomalous results Look at this graph: Which result do you think may be anomalous? A result like this should be taken again, to check it. x x x x x x

13. Types of errors When reading scales, there are 2 main types of error: Let’s look at some examples... Random errors Systematic errors.

14. Random errors These may be due to human error, a faulty technique, or faulty equipment. To reduce the error, take a lot of readings, and then calculate the average (mean).

15. These errors cause readings to be shifted one way (or the other) from the true reading. Systematic errors Your results will be systematically wrong. Let’s look at some examples...

16. Example 1 Suppose you are measuring with a ruler: Systematic errors If the ruler is wrongly calibrated, or if it expands, then all the readings will be too low (or all too high):

17. Example 2 If you have a parallax error: Systematic errors with your eye always too high then you will get a systematic error All your readings will be too high.

18. A particular type of systematic error is called a zero error. Systematic errors Here are some examples...

19. Example 3 A spring balance: Zero errors Over a period of time, the spring may weaken, and so the pointer does not point to zero: What effect does this have on all the readings?

20. Example 4 Look at this top-pan balance: Zero errors There is nothing on it, but it is not reading zero. What effect do you think this will have on all the readings? It has a zero error.

21. Example 5 Look at this ammeter: Zero errors If you used it like this, what effect would it have on your results?

22. Example 6 Look at this voltmeter: Zero errors What is the first thing to do? Use a screwdriver here to adjust the pointer.

23. Example 7 Look at this ammeter: Zero errors What can you say? Is it a zero error? Or is it parallax?

24. Example 8 Look at this ammeter: Zero error, Parallax error What is it for? How can you use it to stop parallax error? It has a mirror behind the pointer, near the scale. When the image of the pointer in the mirror is hidden by the pointer itself, then you are looking at 90 o, with no parallax.

25. In summary Human errors can be due to faulty technique. Systematic errors, including zero errors, will cause all your results to be wrong. Random errors can be reduced by taking many readings, and then calculating the average (mean). Parallax errors can be avoided. Anomalous results can be seen on a graph.

26. Understand the effects of - Human error, including parallax error, - Random errors, - Systematic errors, including zero errors Be able to reduce these errors when doing your practical work Be able to identify anomalous results. Learning Outcomes You should now:

27. For more details, see:  New Physics for You, page 362 For more free PowerPoints, visit  the web-site at www.physics4u.co.uk

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