Practise 45 real questions on Physical quantities and units from 2021 to 2026. See the answer and explanation as soon as you answer.
Physical quantities and units is one of the 13 main topics in our A Level Physics (Cambridge (CAIE) 9702) question bank, and about 7% of its real questions come from it. Tayyari Karo has 45 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2; 39 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 25 medium, 18 easy, 2 hard.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
What is an SI base quantity?
Answer: D. current
The SI base quantities are length, mass, time, current, temperature and amount of substance; ampere and coulomb are units and charge is a derived quantity.
The diameter of a ball is measured as (5.26 ± 0.02) cm.
What is the absolute uncertainty in the volume of the ball?
Answer: B. 0.87 cm³
V = (π/6)d³; fractional uncertainty in V = 3×(0.02/5.26), giving ΔV ≈ 0.87 cm³.
Which calculation produces a vector quantity?
Answer: B. final displacement − initial displacement
Displacement is a vector, so the difference of two displacements is a vector (giving another displacement, i.e. distance moved with direction). The others (charge, power, kinetic energy) are scalars.
Which unit is not an SI base unit?
Answer: C. C (coulomb)
The coulomb is a derived unit (equal to A s), not one of the seven SI base units.
Which term represents a physical quantity?
Answer: D. spring constant
A physical quantity has a numerical magnitude and a unit; spring constant (N m⁻¹) fits this, whereas a metre is a unit, percentage uncertainty is a ratio, and quark flavour is a label.
What is a reasonable estimate of the volume of an adult person?
Answer: A. 0.10 m³
A person of mass ~70 kg and density close to that of water (1000 kg m⁻³) has a volume of about 0.07–0.1 m³.
(a)(i) Define power. [1]
(a)(ii) Use the definition of power to show that the SI base units of power are kg m² s⁻³. [1]
(b) The intensity I of a sound wave moving through a gas is given by I = f²A²vk, where f is the frequency of the wave, A is the amplitude of the wave, v is the speed of the wave, and k is a constant that depends on the gas. Determine the SI base units of k. [3]
(a)(i) Power is the work done per unit time (rate of energy transfer).
(a)(ii) P = W/t, so units of P = units of energy/units of time = kg m² s⁻²/s = kg m² s⁻³.
(b) Intensity I = P/A, so units of I = kg m² s⁻³/m² = kg s⁻³. Units of f = s⁻¹, units of A = m, units of v = m s⁻¹. Rearranging I = f²A²vk gives k = I/(f²A²v), so units of k = kg s⁻³ / [(s⁻¹)² × m² × m s⁻¹] = kg s⁻³ / (m³ s⁻³) = kg m⁻³.
Use base SI units for energy (kg m² s⁻²) and rearrange each formula to isolate the unknown quantity's units.
| Session | Paper 1 | Paper 2 |
|---|---|---|
| May/June 2026 | 4 | – |
| May/June 2025 | 4 | – |
| October/November 2025 | 4 | – |
| May/June 2024 | 4 | – |
| October/November 2024 | 4 | 1 |
| May/June 2023 | 3 | 1 |
| October/November 2023 | 3 | 1 |
| May/June 2022 | 3 | – |
| October/November 2022 | 4 | 1 |
| May/June 2021 | 3 | 1 |
| October/November 2021 | 3 | 1 |
45 real A Level Physics (9702) questions on Physical quantities and units from 2021 to 2026, from Paper 1, Paper 2. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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