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, 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.

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.

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5

25.0 30.0 1.2 1.5

30.0 25.5 1.2 1.1

35.0 23.0 1.2 0.9

40.0 21.3 1.2 0.7

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5

25.0 30.0 1.2 1.5

30.0 25.5 1.2 1.1

35.0 23.0 1.2 0.9

40.0 21.3 1.2 0.7

2.5

1.2

2 s.f.

2 s.f.

This should be 2 s.f.

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5 2.1

25.0 30.0 1.2 1.5

30.0 25.5 1.2 1.1

35.0 23.0 1.2 0.9

40.0 21.3 1.2 0.7

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5 2.1

25.0 30.0 1.2 1.5 1.3

30.0 25.5 1.2 1.1 0.92

35.0 23.0 1.2 0.9

40.0 21.3 1.2 0.7

0.9

1.2

1 s. f.

2 s.f.This should

be 1 s.f.

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5 2.1

25.0 30.0 1.2 1.5 1.3

30.0 25.5 1.2 1.1 0.92

35.0 23.0 1.2 0.9 0.8

40.0 21.3 1.2 0.7

Example of tabley/ cm x/ cm h0/ cm hi/ cm m

20.0 42.0 1.2 2.5 2.1

25.0 30.0 1.2 1.5 1.3

30.0 25.5 1.2 1.1 0.92

35.0 23.0 1.2 0.9 0.8

40.0 21.3 1.2 0.7 0.6

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 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.

Bear these points in mind for Practicals next year!

Study hard for EOY!Check your marks on SDMS!