Cambridge International · AS & A Level · 9702
A-Level Physics
Make sense of the physics. Build the confidence to solve it.
Explore your courseCambridge numbering throughout · AS 1–11 · A2 12–25 Official specification ↗
Selected topic 1: Physical quantities and units
AS Level Topic 1 / 25
1. Physical quantities and units
Quantities, SI units, prefixes and the language of measurement.
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A measurement communicates a quantity, a unit and a limit to precision. Consistent units and an honest uncertainty make a calculated result useful.
Be ready to…
- Convert prefixes and express derived units in SI base units before substituting values.
- Resolve vectors into perpendicular components and distinguish magnitude from direction.
- Estimate measurement uncertainties and propagate them through sums, products and powers.
Key equations 3 relationships
Average speed v is in m s⁻¹ when distance L is in m and elapsed time t is in s; this does not give an instantaneous speed.
Δx is the absolute uncertainty, in the same unit as the non-zero measured value x. The percentage has no physical unit.
For v = L/t, add fractional uncertainties to estimate a maximum uncertainty. This first-order rule assumes uncertainties are small; it is not a statistical standard-error formula.
Work through an example Try it before revealing
A trolley travels (1.20 ± 0.01) m in (0.80 ± 0.02) s. Find its average speed and estimate the maximum absolute uncertainty by adding fractional uncertainties.
Reveal the reasoning and answer
- Calculate the speed: v = 1.20 / 0.80 = 1.50 m s⁻¹.
- Add fractional uncertainties: Δv/v ≈ 0.01/1.20 + 0.02/0.80 = 0.0333, or 3.33%.
- Convert back to an absolute uncertainty: Δv ≈ 1.50 × 0.0333 = 0.05 m s⁻¹.
v = (1.50 ± 0.05) m s⁻¹.
An original revision starter. Use Curriculum alignment below to check the required syllabus depth.
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Explore the central ideas in physical quantities and units.
Open Curriculum alignment below for reviewed section scope. Shared activities and downloads are supplementary resources.
Open lessonCurriculum alignmentAS · exams 2027 · 12 objectives
AS · exams 2027
12 objectives checked: 12 explanations mapped, 0 partial, 0 teaching gaps.
Open an objective to see the required depth, exact lesson section and suitable practice. A mapped explanation does not certify practical competence or every resource on the page.
AS · 1.1.1 Measurement notation Explanation mapped
Required depth: Numbers, units and the meaning of a measured value.
Study this section → The quantity formula and desk-length example connect the number to its unit.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.1.2 Physical estimation Explanation mapped
Required depth: Order-of-magnitude judgement using familiar physical benchmarks.
Study this section → The section teaches benchmark-based estimation, explicit modelling, sensible rounding and plausibility checks; the bag-lifting example works through estimated energy and power.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.2.1 Base-unit fluency Explanation mapped
Required depth: Associate the five relevant base quantities with their SI symbols.
Study this section → The base-unit tabs and current entry list the required quantity/unit pairs.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.2.2 Composite unit construction Explanation mapped
Required depth: Algebraic unit products and quotients, including negative powers.
Study this section → A reusable defining-equation method, a broad AS base-unit table and a worked coefficient-unit example teach products, quotients and powers of units.
Study this section → The newton is expanded into base units; the lesson gives only a small set of derived-unit examples.
Practise this objective · 3 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.2.3 Dimensional equation checks Explanation mapped
Required depth: Compare every additive term and both sides of an equation.
Study this section → The explanation checks every additive term and both sides, distinguishes necessary dimensional agreement from proof, and works a deliberately non-homogeneous alternative.
Study this section → Provides the force-unit starting point, but not a general equation-checking procedure.
Practise this objective · 2 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.2.4 Prefix fluency Explanation mapped
Required depth: Powers of ten in both basic and compound units.
Study this section → All ten required prefixes are in the visible table; squared lengths, mass prefixes and compound conversion are explained and applied in the worked example.
Study this section → Inspected the seven-position prefix array and conversion examples.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.3.1 Measurement bias and scatter Explanation mapped
Required depth: Explain error effects and why repetition cannot remove a fixed bias.
Study this section → The random/systematic cards include repetition, a mis-zeroed balance and removal of a bias source.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.3.2 Accuracy and precision Explanation mapped
Required depth: Distinguish closeness to a reference from agreement of repeated readings.
Study this section → Separate cards distinguish clustered results from results close to the accepted value.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.3.3 Uncertainty propagation Explanation mapped
Required depth: Percentages, absolute intervals and powers; first-order conservative rules.
Study this section → The absolute-sum, percentage-sum and power rules are followed by a checked resistivity example.
Practise this objective · 2 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.4.1 Scalar/vector distinction Explanation mapped
Required depth: Magnitude, direction and familiar physical examples.
Study this section → The comparison section classifies quantities by whether direction is needed.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.4.2 Planar vector arithmetic Explanation mapped
Required depth: Signed components, scale drawings and trigonometry.
Study this section → The component/tip-to-tail model includes a separate reverse-and-add subtraction explanation.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗AS · 1.4.3 Vector resolution Explanation mapped
Required depth: Resolve against named perpendicular axes using sine and cosine.
Study this section → Inspected the two component formulae and angle-controlled vector diagram.
Practise this objective · 1 reviewed question matches →
Official syllabus reference · page 16 ↗Complete Cambridge topic directory All 25 topics →
AS Level foundations
A Level extension
Curriculum & sources Reference information →
Cambridge 9702: scope and course structure
Cambridge 9702 syllabus editions: 2025–2027 and 2028–2030. Select the year in which you will take the examination. AS candidates study Topics 1–11. Full A Level candidates study those foundations plus Topics 12–25, with practical skills assessed throughout.
The 12 visual groups reorganise the existing 25-topic map; they are not official syllabus headings. GioPhysics is an independent learning resource, not an examination board.
Check your specification
- Cambridge 9702 — official specification ↗
- Edexcel 9PH0 — official specification ↗
- AQA 7408 — official specification ↗
- OCR A H556 — official specification ↗
Edexcel, AQA and OCR selections offer shared-topic support, not a complete board-specific course map. Use your exam board’s current specification for required topics, practical work and assessments.