1. Practical Skills

2. A Speed camera takes two images of a moving car and works out speed by calculating distance/time. How do you think this image would help somebody appeal their fine in court?

3. What are Uncertainties?
What do you think this is? It is very old!
It is GRB B and is thought to be the remnants of one of the first stars born after the Big Bang.
It is ± years old

4. Calculating Percentage Uncertainties
Reading on meter =
12.6 V
Finest division =
0.2 V
% Uncertainty = Finest Division x 100
Reading Taken
% Uncertainty = (0.2/12.6) x 100 =
1.6 %

5. Task 1. 3. 100 m record of 9.6 s 4. Extension of 0.002 m (2 mm)
Calculate the percentage uncertainties for the following measurements: 1.
m record of 9.6 s 1%
0.3%
4. Extension of m (2 mm)
50%
5. Extension of m (45 mm) 2% 2.
0.03%

6. Combining Uncertainties
Suppose I want to work out the density of the block…
Mass (kg)
Density =
Volume (m3)
Mass = ± kg
Volume = (6.25 ± 0.25) x 10-5 m3
To Work out the uncertainty in the density, I have to combine the uncertainty in the mass with the uncertainty in the volume

7. How do we do it?
Work out the Percentage Uncertainty in the volume and the mass.
2. Then add these together.

8. Work it out…
Answer…
4.2%

9. THE RULES A x B or A ÷ B A2 An What happens in the formula
What to do to calculate uncertainties
A x B or A ÷ B
Add percentage uncertainty of A with percentage uncertainty in B A2
Double the percentage uncertainty of A An
Multiply the percentage uncertainty by n

10. Independent Learning Task
There is a colour coded question grid on your worksheet. You need to choose 3 questions in a line (can be horizontal, vertical, diagonal, doesn’t have to be through the middle box). Beware however… Blue (easy) to Yellow (taxing) to pink (challenging). Blue questions gain 1 mark, yellow gain 2 and pink gain 3 marks. Make sure you clearly label your answers You have 12 minutes

11. Assessment
Swap your work with your partner and assess each others work using the mark scheme. PINK – 3 MARKS YELLOW – 2 MARKS BLUE – 1 MARK

12. Explaining the difference between accurate and reliable
True value
Imagine we carried out an experiment . The Bulls Eye represents the true value if there were no errors in your experiment.

13. Meaning of accurate and reliable 1
Imagine then – if the first person did this experiment 4 times and got the following results.
The results of this experiment are very close together. The results are reliable but they are NOT ACCURATE because they are far away from the true value.

14. Meaning of accurate and reliable 2
Imagine then – if the second person did this experiment 4 times and got the following results.
Now our results are close to the true value but also very close together around the true value. We say it is both RELIABLE and ACCURATE.

15. Meaning of accurate and reliable 3
Imagine then – if the third person did this experiment 4 times and got the following results.
Now our results are all over the place and not close to the true value. The results are NOT RELIABLE nor are they ACCURATE.

16. Meaning of ANOMALOUS result
Imagine now the first person then did the same experiment for the 5TH time and got the following result.
5th reading – this is an ANOMALOUS result. It doesn’t seem to follow the pattern . We would normally REPEAT this particular result or ignore it when we do an average.
First 4 readings

17. Example of reliable data
Imagine the teacher has carried out the experiment first and used a light gate! The teacher’s value was 3.25s.
Example of reliable data
Student 1 result:
Height parachute dropped from (m)
Time taken to drop height - 1st reading
(seconds)
Time taken to drop height - repeat 1
Time taken to drop height - repeat 2
Time taken to drop height - repeat 3
1.0
3.5
3.3
3.1
the data are reliable because they are very close together. It is also accurate because it is close to the answer that is expected.
Close together

18. Example 2 Anomalous result
The teachers value was 3.25 seconds.
Student 2 result:
Height parachute dropped from
(m)
Time taken to drop height - 1st reading
(seconds)
Time taken to drop height - repeat 1
Time taken to drop height - repeat 2
Time taken to drop height - repeat 3
1.0
3.5
3.4
3.3
8.2
Far away from the others
This set of data is still reliable - we can be pretty sure that the answer that we are looking for lies near 3.x but there is an anomalous result which will skew the average towards a higher value than it really is in this case.
Average will be higher than it actually is

19. Example 2 Anomalous result
To correct this mistake we can either repeat the last mistake or ignore it when we work out an average.
Example 2 Anomalous result
Height parachute dropped from (m)
Time taken to drop height - 1st reading
(seconds)
Time taken to drop height - repeat 1
Time taken to drop height - repeat 2
Time taken to drop height - repeat 3
1.0
3.5
3.4
3.3
Result ignored
By removing the anomalous – the average value will move closer to the true value i.e. it will become more accurate
Average will be more accurate when anomalous is removed

20. Meaning of accurate and reliable 3
The teachers value was 3.25s.
Meaning of accurate and reliable 3
Student 3 result:
Height parachute dropped from (m)
Time taken to drop height - 1st reading
(seconds)
Time taken to drop height - repeat 1
Time taken to drop height - repeat 2
Time taken to drop height - repeat 3
1.0
1.5
6.4
5.3
2.2
Results are all over the place
The results are NOT RELIABLE nor are they ACCURATE.

21. Precision in Instruments
Which one is the odd one out?

22. Graph Work Voltage (V) Current (A) 1,00 0,17 2,00 0,43 3,00 0,62 4,00
0,86
5,00
1,06
6,00
1,21
7,00
1,43
8,00
1,58
:Plot a graph of the following data: