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Review for PR 9

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

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Review for PR 9

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  1. Review for PR 9 Pointers to note from your PR 9

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

  3. 2. Table of data • Units • Remember that x, y, h0, hi 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.

  4. 2. Table of data • In this experiment, y/cm, x/cm, h0/cm and hi/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.

  5. Example of table

  6. Example of table This should be 2 s.f. 2 s.f. 2.5 1.2 2 s.f.

  7. Example of table

  8. Example of table 1 s. f. 0.9 This should be 1 s.f. 1.2 2 s.f.

  9. Example of table

  10. Example of table The number of sig fig is dependent on those particular values used to calculate that one specific value of m.

  11. 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!

  12. 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!

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

  14. 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.

  15. 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.

  16. 5. Sources of error • Example 2: • The precision of the ruler is only 0.1 cm, but the smallest hi 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.

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

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