Measurement, units and uncertainty
Answer in the spaces provided. Marks are shown in brackets; the parts follow the four MYP Sciences criteria. Use the mark scheme only after you have tried every question.
APart A — Knowing and understanding
Criterion A · 12 marks
1
State the SI base units of mass and electric current.[2 marks]
2
Write these numbers in standard form: (i) 38 000 000 m (ii) 0.000 072 s.[2 marks]
3
Convert: (i) 450 mA to A (ii) 2.5 GW to W (iii) 80 cm2 to m2.[3 marks]
4
Explain the difference between an accurate set of readings and a precise set of readings.[2 marks]
5
A student measures the length of a wooden block with a ruler marked in millimetres, but reads the scale at an angle each time.
(a)
Name the type of error this causes and explain why taking more readings will not remove it.[2 marks]
(b)
State the uncertainty in a single reading from this ruler.[1 mark]
BPart B — Inquiring and designing
Criterion B · 7 marks
A pendulum is a mass hanging on a string. A student wants to find out how the length of the string affects the time for one swing (the period). A stopwatch reads to 0.01 s.
6
Write a research question for this investigation.[1 mark]
7
Identify the independent variable, the dependent variable and one control variable, and say how the control variable will be kept the same.[3 marks]
8
A single swing lasts under 2 s, but human reaction time is about 0.2 s. Explain how the student should time the swings to reduce the uncertainty in the period.[3 marks]
CPart C — Processing and evaluating
Criterion C · 9 marks
A student hangs loads on a spring and measures its extension.
| Load / N | 0 | 1.0 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 |
|---|---|---|---|---|---|---|---|
| Extension / cm | 0.0 | 2.1 | 3.9 | 6.0 | 9.5 | 10.1 | 11.9 |
9
Plot a graph of extension (y-axis) against load (x-axis) and draw a line of best fit.[4 marks]
10
Identify the anomalous result.[1 mark]
11
Use your line to find the gradient, with its unit.[2 marks]
12
Describe the relationship between load and extension, with a reason from the graph.[2 marks]
DPart D — Reflecting on the impacts of science
Criterion D · 4 marks
13
In 1999 a spacecraft was lost because two engineering teams used different units for the same quantity. Discuss why the international scientific community uses one agreed system of units. Include at least one advantage and one limitation or difficulty.[4 marks]
Mark scheme — 32 marks
1 [2]
- kilogram (kg) [1]
- ampere (A) [1]
2 [2]
- (i) \( 3.8 \times 10^{7} \) m [1]
- (ii) \( 7.2 \times 10^{-5} \) s [1]
3 [3]
- (i) 0.45 A [1]
- (ii) \( 2.5 \times 10^{9} \) W [1]
- (iii) 1 m2 = 104 cm2, so 80 cm2 = 0.008 m2 (\( 8 \times 10^{-3} \) m2) [1]
4 [2]
- Accurate: close to the true value [1].
- Precise: readings close to each other / small spread [1].
5(a) [2]
- Systematic error (parallax) [1].
- Every reading is shifted in the same direction, so averaging does not cancel it [1].
5(b) [1]
\( \pm 0.5 \) mm (half the smallest division) [1].
6 [1]
For example: “How does the length of a pendulum string (m) affect its period (s)?” Must name both the independent and dependent variable [1].
7 [3]
- Independent: length of string [1].
- Dependent: period / time for one swing [1].
- Control, with how: e.g. same mass bob (use the same bob throughout), same release angle (use a protractor), same string [1].
8 [3]
- Time many swings, e.g. 10 or 20, in one measurement [1].
- Divide the total time by the number of swings [1].
- The reaction-time error is shared across all the swings, so the percentage uncertainty in the period is much smaller; repeat and average for further improvement [1].
9 [4]
- Axes the right way round, labelled with units [1].
- Sensible linear scales using more than half the grid [1].
- All points plotted to within half a small square [1].
- Straight best-fit line through the origin, ignoring the anomaly [1].
10 [1]
The reading at 4.0 N (9.5 cm) [1].
11 [2]
- Large triangle on the line, e.g. 12.0 cm ÷ 6.0 N [1].
- About 2.0 cm/N (accept 1.9–2.1) [1].
12 [2]
- Extension is directly proportional to load [1].
- Because the best-fit line is straight and passes through the origin [1].
13 [4]
- Advantage: results can be shared and compared worldwide without conversion errors [1].
- Relevant example or consequence, e.g. safety, cost of errors in engineering or medicine (drug doses in mg vs µg) [1].
- Limitation/difficulty: some countries and industries still use other units (feet, pounds, inches in aviation), so conversion is still needed; changing systems is costly [1].
- A reasoned concluding judgement [1].
For Parts B–D, credit any scientifically valid answer that meets the same point; the answers given are models, not the only acceptable wording.