The questions are on the SI units test. Take it under real conditions before reading the mark scheme.
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. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on SI units, from SI base units to unit conversion, with the equivalent answers to accept.
Marks are shown for each part. Method marks are given even when a final answer is wrong, as long as the working is clear, so always show your steps and give the unit.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE WS, IGCSE 1.1
Question 2 Prefixes (2 marks)
- 3.6 MHz = 3.6 × 10⁶ Hz.
- 250 × 10⁻⁶ m = 2.5 × 10⁻⁴ m.
Marking: 1 mark each; the standard form must have a from 1 up to (not including) 10.
Question 3 Standard form (2 marks)
- 8.3 × 10⁻⁴ s.
- 60 200.
Marking: 1 mark each.
Question 4 Significant figures and reading (3 marks)
- 4 significant figures.
- 4.10.
- 7.4 cm (resolution 1 mm).
Marking: 1 mark each; 4.1 alone loses the mark in (b).
Question 5 Area of a field (3 marks)
Area = 24.5 × 8.2 = 200.9 m². The width has 2 s.f., so the area is 2.0 × 10² m².
Marking: 1 mark for the product, 1 mark for rounding to 2 s.f., 1 mark for standard form with the unit.
Question 6 Precision and accuracy (3 marks)
- Student X: the mean 50.0 g equals the true value.
- Student Y: the range is 0.1 g, against 0.2 g for X.
- A systematic error such as a zero error on the balance, which adds about 2 g to every reading.
Marking: 1 mark each part.
Question 7 Mean and uncertainty (3 marks)
Mean = (2.31 + 2.35 + 2.29 + 2.33) ÷ 4 = 9.28 ÷ 4 = 2.32 s. Uncertainty = (2.35 − 2.29) ÷ 2 = 0.03 s. Percentage = 0.03 ÷ 2.32 × 100 = 1.3 %.
Marking: 1 mark for the mean, 1 mark for the uncertainty, 1 mark for the percentage.
Question 8 Unit conversion (2 marks)
72 × 1000 ÷ 3600 = 20 m/s.
Marking: 1 mark for the method (× 1000, ÷ 3600), 1 mark for 20 m/s.
