The method and the results are on the SI units lab. Do the analysis yourself first, then check the answers below.
Quick answer: SI units are the internationally agreed units for measurement: metre for length, kilogram for mass, second for time, ampere for current and kelvin for temperature. These answers go with the Physics 9-10 lab on SI units: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
The model answers use the sample table. Your own values will differ slightly, but the pattern should be the same: the tallest stack gives the smallest percentage uncertainty.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE WS, IGCSE 1.1
Question 1 Thickness of one sheet
1. 2.2 ÷ 20 = 0.110 mm; 4.1 ÷ 40 = 0.103 mm; 6.3 ÷ 60 = 0.105 mm; 8.0 ÷ 80 = 0.100 mm; 10.2 ÷ 100 = 0.102 mm.
2. Mean = (0.110 + 0.1025 + 0.105 + 0.100 + 0.102) ÷ 5 = 0.5195 ÷ 5 = 0.104 mm.
Question 2 Percentage uncertainty
20 sheets: 0.5 ÷ 2.2 × 100 = 23 %.
100 sheets: 0.5 ÷ 10.2 × 100 = 4.9 %.
Question 3 Choosing the best stack
The reading error of ±0.5 mm is the same for every stack, but it is a much smaller fraction of a tall stack. The 100-sheet stack has a percentage uncertainty of about 5 %, against 23 % for 20 sheets, so it gives the most reliable value.
Question 4 Graph and gradient
The points lie close to a straight line through the origin: the height is directly proportional to N. Gradient = 10.2 mm ÷ 100 sheets = 0.102 mm per sheet.
Question 5 Metres in standard form
0.102 mm = 0.102 × 10⁻³ m = 1.02 × 10⁻⁴ m.
Question 6 Checking against a reference
5 % of 0.102 mm is 0.005 mm, so the result is 0.102 ± 0.005 mm, which spans 0.097 to 0.107 mm. The micrometer value of 0.10 mm lies inside this range, so the two results agree.
Question 7 Improving the method
1. Use a micrometer on the stack, or a stack of 500 sheets, to cut the percentage uncertainty.
2. Press every stack with the same book for the same time, and check the ruler has no worn end, to avoid a systematic error.
