# Review for PR 9 Pointers to note from your PR 9. 1. Approx focal length Check correct unit (cm) You used a metre rule to measure, so it should be given.

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Review for PR 9 Pointers to note from your PR 9

1. Approx focal length Check correct unit (cm) You used a metre rule to measure, so it should be given to 1 decimal place!

2. Table of data Units – Remember that x, y, h 0, h i are all in cm – Magnification, m, does not have units (X is not a unit for magnification!!) Measured data – Data you obtain from measurements must be recorded to the appropriate decimal place based on the instrument used.

2. Table of data – In this experiment, y/cm, x/cm, h 0 /cm and h i /cm are all measured values. They must all be recorded to 1 decimal place. Calculated value – The only calculated value for this experiment is m! – m must follow the least number of s.f. of values used to calculate it.

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.5 25.030.01.21.5 30.025.51.21.1 35.023.01.20.9 40.021.31.20.7

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.5 25.030.01.21.5 30.025.51.21.1 35.023.01.20.9 40.021.31.20.7 2.5 1.2 2 s.f. This should be 2 s.f.

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.52.1 25.030.01.21.5 30.025.51.21.1 35.023.01.20.9 40.021.31.20.7

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.52.1 25.030.01.21.51.3 30.025.51.21.10.92 35.023.01.20.9 40.021.31.20.7 0.9 1.2 1 s. f. 2 s.f. This should be 1 s.f.

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.52.1 25.030.01.21.51.3 30.025.51.21.10.92 35.023.01.20.90.8 40.021.31.20.7

Example of table y/ cmx/ cmh 0 / cmh i / cmm 20.042.01.22.52.1 25.030.01.21.51.3 30.025.51.21.10.92 35.023.01.20.90.8 40.021.31.20.70.6 The number of sig fig is dependent on those particular values used to calculate that one specific value of m.

3. Graph S – Scale (data points need to cover at least 5 big squares horizontally and 6 big squares vertically) P – Points are correctly plotted to get this point L – A good best fit line is drawn (also depends on whether the line is neat) A – Label axes properly!

3. Graph C – Choose points OTHER THAN your own data points. – Write coordinates to the precision of the graph paper (don’t round up to 3 s.f.!! Leave it to the most precise value you can determine in the graph) T – Triangle has to be big enough! – Use dotted lines!

Example of Graph First data point Last data point These points must be more than 5 big squares apart Similarly for vertical, the first and last data points must be more than 6 big squares apart

4. Precaution Must have two parts: – Action taken – How it helps to make your results better – Which particular reading does it improve Example: – Switch off the lights so that the image formed will be clearer and thus, the determination of x will be more accurate.

5. Sources of error Must have 2 parts – Describe the difficulty you faced in the experiment – State which measurement it affects (measurement of x, y, or h) Example 1: – It is difficult to determine when the sharpest image is formed. The image remains focused over a range of x values. Therefore, the error in the measurement of x values is significant.

5. Sources of error Example 2: – The precision of the ruler is only 0.1 cm, but the smallest h i reading required to be measured is 0.4 cm. The percentage of uncertainty is about 25%. Thus, the precision of the ruler causes a significant source of error.

Bear these points in mind for Practicals next year! Study hard for EOY! Check your marks on SDMS!

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