# SPA

### Skill 1 & 2

1. Spend about 3-5 min reading question.  Take note of important points and variables to be changed and measured.

2. First task –> to draw tables and columns with headings, units and number of d.p or s.f (written in pencil above the column [area outside the table]).  Each data set carried out from the experiment must be transferred to the table. But do not do calculation at this point!

3. Collect and record all data from experiment.  Process [do calculation to obtain value for other columns in the table] data only after ALL measurements are taken.

4. All students should have sharp pencil, clear ball point pen (do not use to plot graph), calculator and 30 cm long transparent ruler to plot graph.

it. Gradient computed to be 3 s.f.

6. If x-axis (horizontal axis) starts from zero, y intercept can be read off from graph and to have same accuracy as y values. Y intercept to have same units as y values.

7. If x-axis does not start from zero, y intercept to be computed from
y=mx+c. Y intercept to be 3 s.f in this case and to have same units as y
values.

8. Graph to be at least 50 percent of graph paper.

9. Size of 1 cross (data point) to be size of 1 small graph paper grid.

10. Line of best fit to draw graph (refer to workbook for explanation of line of best fit)

11. Need NOT start x and y axes from zero unless specified in question.

12. Appropriate scale – Do not use 2 cm to represent 3 units, 6 units or 7 units and their multiples.

13. Label x and y axes with units

14. Measured values to follow accuracy of instrument (eg. length measurements to record to 1 decimal place)

15. Computed values/processed data are written to 3 s.f.

16. Identify 2 key sources of errors if asked in question (common errors in practical)

17. ALWAYS calculate the y-intercept in order to conclude the relationship. Unit must be present for the y-intercept value. Eg. a varies linearly with b OR a is linearly related to b #if y-intercept is non zero

Terms to use: linearly (straight line that doesn’t pass through the origin) , non-linearly related (curve), directly proportional (cut through origin).

18. Setting up and data collecting should not take more than 20 minutes.

19. Raise hand to alert invigilator to mark intermediate step if specified in question

20. At least 5 set of data points in the table unless question specifies otherwise.

How to plot a graph –> Link 1

### Skill 3

1. Plan an investigation
• Make a clear statement of the problem which serves the purpose of the task. Try asking yourself if what you are investigating will answer or provide a mean to conclude particular relationship which is related to what the task is asking you to do.
• In any investigation or experiment, you will always need to keep other factors besides those that you are changing (recall: IV, DV) constant. These factors/variables are called control variables. They must be measurable and not feature of the provided apparatus. If you tell someone else that you want to keep this particular variable constant and the person replies you with a “duh! Obviously!” then it is probably a poor choice of control variable. E.g if you want to study how different races react to anger, then you must ensure that other factors such as who are around and what time of the day etc constant.
• Control variables should be mentioned before you even begin to think about your procedure to investigate the relationship of IV and DV you identify in your problem statement. Isn’t that logical?
1. Producing a procedure for the investigation
• Select appropriate apparatus and provide a clear and well labelled diagram of your set up as certain things are hard to explain in words. Approximately 10 cm x 10cm should be large enough to be seen with comfort.
• Step-by-step instruction on how to carry out the experiment. Indicate clearly what variable you are changing and what variable will be affected. Describe how these changes can be collected and processed. You can provide a table with headings of what are your IV and DV and how to process the information in order to deduce the relationship. However, you do not need to come up with fake data in order to covey your ideas.