AS Level Physics notes (Cambridge 9702)

By The STEM-Tutor team · Updated October 2026

These notes cover the 11 AS Level topics in Cambridge International AS and A Level Physics (9702). They are tested in Papers 1, 2 and 3, and assumed knowledge for the full A Level. Each section gives the key ideas, equations and the points examiners look for.

1. Physical quantities and units

• SI base units: kilogram, metre, second, ampere, kelvin and mole. Derived units are combinations, for example the newton is kg m s⁻².
• Homogeneity: every term in a valid equation has the same base units, which lets you check equations.
• Errors and uncertainties: random errors scatter readings and are reduced by repeating; systematic errors shift all readings and are not removed by averaging. Precision is about scatter; accuracy is closeness to the true value.
• Combining uncertainties: add absolute uncertainties for sums and differences; add percentage uncertainties for products and quotients; multiply the percentage uncertainty by the power for powers.
• Scalars and vectors: add vectors by triangles or components; resolve a vector into two perpendicular components.

2. Kinematics

• Displacement, velocity and acceleration are vectors. The gradient of a displacement-time graph is velocity; the gradient of a velocity-time graph is acceleration and the area under it is displacement.
• The equations for uniformly accelerated motion: v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t.
• Projectiles: treat horizontal motion (constant velocity) and vertical motion (acceleration g) separately.

3. Dynamics

• Newton's laws; F = ma for constant mass, and more generally force = rate of change of momentum.
• Momentum p = mv is conserved in all collisions. In elastic collisions kinetic energy is also conserved, and the relative speed of approach equals the relative speed of separation.
• Weight, friction, drag and terminal velocity: an object falling through a fluid reaches terminal velocity when drag plus upthrust equals weight.

4. Forces, density and pressure

• Moments: moment = force × perpendicular distance; a couple produces a torque. For equilibrium, the resultant force and the resultant moment are both zero.
• Density ρ = m / V; pressure p = F / A; pressure in a fluid Δp = ρgΔh.
• Upthrust comes from the pressure difference across an object in a fluid, and equals the weight of fluid displaced (Archimedes' principle).

5. Work, energy and power

• Work done W = Fs cos θ; work done by a gas at constant pressure is pΔV.
• Kinetic energy ½mv²; change in gravitational potential energy mgΔh in a uniform field.
• Power P = W / t = Fv; efficiency = useful output ÷ total input.

6. Deformation of solids

• Hooke's law: F = kx up to the limit of proportionality. Elastic deformation is reversed when the load is removed; plastic deformation is not.
• Stress = F / A, strain = extension / original length, and the Young modulus = stress / strain.
• Elastic potential energy = ½Fx = ½kx², the area under a force-extension graph.

7. Waves

• Progressive waves transfer energy: amplitude, wavelength, frequency, period and phase difference; v = fλ; intensity is proportional to amplitude squared.
• Transverse and longitudinal waves; polarisation applies only to transverse waves, with Malus's law I = I₀cos²θ.
• The Doppler effect for sound from a moving source; the electromagnetic spectrum, with all EM waves travelling at 3.00 × 10⁸ m s⁻¹ in a vacuum.

8. Superposition

• Stationary waves form from two waves travelling in opposite directions, with nodes and antinodes; adjacent nodes are half a wavelength apart.
• Diffraction is greatest when the gap is similar to the wavelength. Two-source interference needs coherent sources; for double slits, λ = ax / D.
• Diffraction gratings: d sin θ = nλ.

9. Electricity

• Current I = ΔQ / Δt; in a conductor I = Anvq.
• Potential difference V = W / Q; resistance R = V / I; power P = VI = I²R = V²/R.
• Resistivity: R = ρL / A. I-V characteristics of a metallic conductor, a filament lamp, a diode, a thermistor and a light-dependent resistor.

10. D.C. circuits

• E.m.f. is energy converted from other forms to electrical per unit charge; p.d. is electrical energy converted to other forms per unit charge.
• Internal resistance: E = I(R + r), so the terminal p.d. falls as the current rises.
• Kirchhoff's first law (charge is conserved) and second law (energy is conserved); resistors in series and parallel; potential dividers.

11. Particle physics

• The nuclear atom from alpha-particle scattering; nucleons, nucleon number A and proton number Z; isotopes.
• Alpha, beta-minus, beta-plus and gamma radiation; antineutrinos and neutrinos in beta decay.
• Fundamental particles: quarks (up, down, strange and others) and leptons. Protons are uud and neutrons udd; in beta-minus decay a down quark becomes an up quark.

Kinematics: a projectile

A ball is kicked horizontally at 12 m s⁻¹ from a ledge 5.0 m high. Taking g = 9.81 m s⁻², how far from the ledge does it land?

• Vertical: 5.0 = ½ × 9.81 × t², so t = 1.01 s.
• Horizontal: 12 × 1.01 = 12 m (2 s.f.).

Uncertainty: a product

A wire's diameter is 0.50 ± 0.01 mm. What is the percentage uncertainty in its cross-sectional area?

• Percentage uncertainty in d = 0.01 / 0.50 × 100 = 2%.
• A = πd²/4, so the percentage uncertainty doubles: 4%.

Diffraction grating

Light of wavelength 600 nm falls on a grating with 500 lines per mm. Find the angle of the first-order maximum.

• d = 1 / 500 mm = 2.0 × 10⁻⁶ m.
• sin θ = λ / d = 600 × 10⁻⁹ / 2.0 × 10⁻⁶ = 0.30, so θ = 17.5°.

How to use these notes

1. Use each section as a checklist, then answer past paper questions on it from the 9702 past papers.
2. Learn definitions word for word: the examiner reports show what earns the mark.
3. Practise Paper 1 multiple choice for speed and Paper 3 skills (tables, graphs, uncertainties) all year.
4. See our 9702 syllabus guide for how the papers work.

Common mistakes

• Confusing e.m.f. with terminal potential difference.
• Adding absolute uncertainties when quantities are multiplied.
• Forgetting that only transverse waves can be polarised.
• Mixing up nodes and antinodes in stationary waves.

Practice questions

Try each one before opening the answer.

Frequently asked questions

Are these notes enough for the AS exams?

They cover the AS content, but you also need practice with past papers, the data and formulae page and Paper 3 practical skills.

Is particle physics on the AS syllabus?

Yes. Topic 11, particle physics, is part of AS Level in 9702.

Do these topics appear in Paper 4?

Paper 4 tests the A Level topics, but AS knowledge is assumed, so these topics come up again.

Key takeaways

• 11 AS topics, from units to particle physics.
• Tested in Papers 1, 2 and 3.
• Learn definitions precisely.
• Uncertainties and graphs matter in every paper.
• Practise with 9702 past papers.

Related guides

• Cambridge 9702 syllabus
• 9702 past papers
• The equations of motion
• Kirchhoff's laws