H2 Physics Definitions and Formulae 2026 (9478) | Data, Constants, What to Memorise
Study guide/
H2 Physics Definitions and Formulae 2026 (9478) | Data, Constants, What to Memorise
In one line
The SEAB Data and Formulae pages give many standard relationships, but you still need to know definitions, graph meanings, assumptions, and when each formula applies.
Key points
Use this page as a topic-by-topic checklist: definition first, equation second, exam condition third.
When revising, test yourself by covering the right-hand side of each section and explaining the quantity in words before writing the formula.
Planning a revision session? Use our study places near me map to find libraries, community study rooms, and late-night spots.
Read in layers
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Read the summary above.
10 seconds
Scan the first few sections below.
100 seconds
Jump into the section that matches your decision.
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Quick revision map
Concrete example: what "know the formula" really means
Contents
Q: What does this H2 Physics definitions and formulae guide cover? A: It is the revision companion for the exact definitions, equations, and constants you still need after SEAB's printed Data and Formulae pages. Use it to memorise what the paper does not provide and to keep the H2 Physics formula sheet in revision-ready form.
TL;DR
The SEAB Data and Formulae pages give many standard relationships, but you still need to know definitions, graph meanings, assumptions, and when each formula applies.
Use this page as a topic-by-topic checklist: definition first, equation second, exam condition third.
When revising, test yourself by covering the right-hand side of each section and explaining the quantity in words before writing the formula.
Looking for the exam-provided formula sheet or data booklet? The official SEAB Data and Formulae pages, printed inside Papers 1-3, list only the standard relationships and constants. Our dedicated H2 Physics Formula Sheet & Data Booklet 2026 guide explains exactly what the exam gives you vs what you still need to memorise. This page is the revision companion for everything else - definitions, derivations, and topic context.
Aligned with the SEAB H2 Physics syllabus (9478, examinations from 2026); use the syllabus Data & Formulae pages and the SEAB 9478 Physics Excel Reference Guide as the ground truth for symbols, units, constants, and spreadsheet workflows.
Status: SEAB's current H2 Physics (9478) syllabus PDF is labelled for 2026, and the linked Physics Excel Reference Guide is version 0.3 for examinations from 2026. Data and Formulae pages are listed as pp. 41-42 of the syllabus and printed as pages 2-3 in Papers 1-3.
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Read time
What to take away
1 second
A formula is useful only when you know its meaning, units, graph link, and conditions.
10 seconds
Use this page as a definition-first checklist. Say the concept in words, then write the equation, then state when it applies.
Example: velocity is the rate of change of displacement; on a displacement-time graph, its value is the gradient, and the sign shows direction.
Quick revision map
What you are trying to recall
Start with this
Then check
Definition
The quantity in words
Whether your wording names the changing quantity
Formula
Symbols and units
Whether the formula needs a special condition
Graph
Gradient and area
Whether the axes are the right way round
Practical uncertainty
Absolute, fractional, or percentage uncertainty
Whether the operation is add/subtract or multiply/divide
Concrete example: what "know the formula" really means
For velocity, do not stop at "v equals s over t". A stronger revision answer is:
Velocity is the rate of change of displacement. On a displacement-time graph, the gradient gives velocity. The sign matters because displacement is directed.
That one answer covers the definition, graph link, and common sign mistake. This is the level of recall needed for short explanation marks.
Contents
Measurement and Uncertainty
Kinematics
Forces, Moments and Equilibrium
Fluids
Newton's Laws, Momentum, Work-Energy-Power
Circular Motion
Gravitation and Orbits
Oscillations and SHM
Waves and Superposition
Resolution and Standing Waves
Thermal Physics and Kinetic Theory
Electric Current, Circuits and Materials
Electric Fields and Potential
Magnetism and Electromagnetic Induction
Quantum and Atomic Physics
Nuclear Physics and Radioactivity
References
1 Measurement and Uncertainty
SI base quantities: mass (kg), length (m), time (s), current (A), temperature (K), amount (mol), luminous intensity (cd). Derived units: formed by products or quotients of base units.
Prefixes: kilo k, mega M, giga G, milli m, micro μ, nano n, pico p.
Accuracy: closeness to true value. Precision: tight scatter in repeats (small random error).
Random error: causes scatter about the mean, reduced by averaging. Systematic error: shifts all readings up or down, not reduced by averaging; remove cause.
Products or quotients: Δy/y≈Δa/a+Δb/b if y=ab or y=a/b.
Powers: Δy/y≈∣p∣Δa/a if y=ap.
Exam check: Define with quantities, not units. For speed, write "distance per unit time", not "distance per second".
2 Kinematics
Distance: total path length. Displacement: directed distance from start to end. Speed: rate of change of distance. Velocity v: rate of change of displacement. Acceleration a: rate of change of velocity.
Hooke's law (small extension): F=kx. Elastic potential energy: Eel=0.5kx2.
Friction: contact force opposing relative motion or its tendency. 9478 requires qualitative treatment only; coefficients of friction (μs, μk) are not in the syllabus. Moment about a point: τ=rFsinθ. Couple: equal, opposite, parallel forces separated by distance d; torque τ=Fd.
Equilibrium (rigid body): ∑F=0 and ∑τ=0. Three-force equilibrium: lines of action intersect at a point. Centre of gravity: single point through which weight acts.
4 Fluids
Upthrust (buoyant force): upward force on a body fully or partially immersed in a fluid. 9478 Topic 2 requires a qualitative treatment only - hydrostatic pressure derivation (p=ρgh) and Archimedes' principle numerical calculations are not in the H2 syllabus. These appear in O-Level Physics and H3 Physics but are not examinable under 9478.
5 Newton's Laws, Momentum, Work-Energy-Power
Newton 1: a body stays at rest or moves uniformly unless a resultant force acts. Newton 2: ∑F=ma. Newton 3: forces between two bodies are equal, opposite, collinear, and act on different bodies.
Momentum: p=mv. Impulse: J=∫Fdt=Δp (area under F−t).
Collisions in isolation: momentum conserved.
Elastic: total KE conserved, relative speed of approach equals separation.
Inelastic: KE not conserved (perfectly inelastic if bodies stick).
Work: W=F⋅s=Fscosθ. Kinetic energy: Ek=0.5mv2. GPE near Earth: ΔEg=mgΔh. Power: P=dW/dt=Fv. Efficiency: useful output over input.
Weight: W=mg. Apparent weightlessness in free fall: normal reaction is zero.
6 Circular Motion
Angular displacementθ (radians), arc length s=rθ. Period and frequency: T=1/f. Angular speed: ω=2πf=2π/T. Tangential speed: v=ωr.
SHM definition: a=−ω2x. General solution: x=Acos(ωt+ϕ). Energies: Ek=0.5mω2(A2−x2), Ep=0.5mω2x2, total =0.5mω2A2.
Special cases:
Mass-spring: ω=k/m.
Simple pendulum (small angle): ω=g/L.
Damping: light (oscillatory decay), critical (fastest non-oscillatory return), heavy (slow, non-oscillatory). Forced oscillations and resonance: steady-state at driving frequency; peak amplitude at resonance; damping lowers and broadens the peak, resonant frequency shifts slightly lower.
9 Waves and Superposition
Progressive wave: transports energy via oscillations. Transverse: oscillations perpendicular to propagation. Longitudinal: oscillations parallel to propagation.
Harmonic form: y(x,t)=Asin(kx−ωt+ϕ) with k=2π/λ, ω=2πf. Speed: v=fλ=ω/k. Intensity: power per area; for the same medium I∝A2.
Polarisation: restricts transverse oscillations to one plane. Malus' law: I=I0cos2θ.
Diffraction: spreading when aperture is comparable to λ. Superposition: resultant displacement is the vector sum. Coherence: constant phase difference. Interference: constructive if path difference is mλ, destructive if (m+0.5)λ.
Young double-slit: fringe spacing x=λD/a (slit separation a, screen distance D). Diffraction grating: maxima satisfy dsinθ=mλ.
10 Resolution and Standing Waves
Rayleigh criterion: two point images are just resolved when one central maximum coincides with the other's first minimum. Approximate angular resolution θ≈1.22λ/D for a circular aperture of diameter D.
Standing wave: two identical counter-propagating waves form fixed nodes and antinodes, with no net energy transport.
Nodes: zero displacement. Antinodes: maximum amplitude.
Strings (fixed-fixed): L=nλ/2.
Air columns: open-open L=nλ/2; closed-open L=(2n−1)λ/4.
Sound: pressure variation is max at displacement nodes, min at displacement antinodes.
11 Thermal Physics and Kinetic Theory
Internal energy U: microscopic KE plus PE; state function. Thermal equilibrium: no net heat flow. Mole: Avogadro number of particles, about 6.022×1023.
Ideal gas: pV=nRT=NkT. Mean KE per molecule: Ek,avg=1.5kT.
First law (this sign convention): ΔU=Q+Won. Processes: isochoric (V constant), isobaric (p constant), isothermal (T constant), adiabatic Q=0.
Specific heat capacity: energy to raise unit mass by 1 K (no phase change). Latent heats: fusion (solid to liquid), vaporisation (liquid to gas). Boiling: temperature constant because heat increases PE. Evaporation cooling: fastest molecules escape, average KE drops.
Why Lv>Lf: vaporisation involves larger PE increase and expansion work.
12 Electric Current, Circuits and Materials
Charge and current: I=dQ/dt. Microscopic current: I=nAvdq.
Emf: energy gained per unit charge from a source around a complete circuit. Potential difference: energy converted per unit charge between two points.
NTC thermistor: resistance decreases as temperature rises.
LDR: resistance decreases with light intensity.
Internal resistancer: terminal pd V=ε−Ir; with load R: I=ε/(R+r).
Series and parallel: Rs=R1+R2+…; 1/Rp=1/R1+1/R2+…. Potential divider (two resistors): Vout=VinR2/(R1+R2)
Measuring ε: use a high-impedance voltmeter (e.g. digital multimeter, typically 10 MΩ) across the cell under no-load conditions; reducing current draw minimises the terminal-pd drop Ir. Note: the potentiometer / null-balance method was in 9749 Topic 15 but has been removed from 9478 - use voltmeter readings with internal-resistance correction instead.
13 Electric Fields and Potential
Coulomb's law (point charges): F=(1/(4πε0))Q1Q2/r2. Field strength: E=F/q; for point charge E=(1/(4πε0))Q/r2 Potential: V=W/q; for point charge V=(1/(4πε0))Q/r. Relation: E=−∇V; uniform field E=V/d.
Conductors in electrostatic equilibrium: E=0 inside, charges on surface. Equipotentials: surfaces of constant V, everywhere perpendicular to E. Potential energy: U=qV. Electron-volt: 1 eV = 1.602 x 10^-19 J.
14 Magnetism and Electromagnetic Induction
Magnetic flux densityB (tesla). Force on current: F=Iℓ×B so F=BIℓsinθ. Force on charge: F=qv×B so F=Bqvsinθ.
Uniform B, perpendicular entry: circular motion with r=mv/(qB), cyclotron frequency ω=qB/m.
Velocity selector (crossed E and B): v=E/B.
Magnetic flux: Φ=BAcosθ; flux linkage: NΦ. Faraday-Lenz: ε=−NdΦ/dt (minus sign indicates opposition). Motional emf: ε=Bℓv when v⊥B.
Eddy currents: circulating currents in bulk conductors cause heating; laminations reduce losses.
AC (sinusoidal): Irms=I0/2, Vrms=V0/2; average power P=VrmsIrms for a resistive load.
Transformers (ideal): Vp/Vs=Np/Ns, Ip/Is=Ns/Np, Pp=Ps. Requires AC to sustain changing flux.
15 Quantum and Atomic Physics
Photoelectric effect: emission of electrons when light frequency is sufficiently high. Observations: threshold frequency f0; intensity controls current, not Ek,max; emission is prompt; Ek,max increases with f.
Atomic energy levels: discrete bound energies; excitation by inelastic collisions or photon absorption; emission/absorption spectra from transitions. For a transition from Ei to Ef, photon energy hf=Ei−Ef.
Wavefunctions: state of a particle represented by ψ; ∣ψ∣2 is the probability density (normalises to 1 over all space). Standing-wave solutions ψn for a particle in a one-dimensional infinite square well of width L give quantised energies En=n2h2/(8mL2).
Note: X-ray spectra (characteristic lines + bremsstrahlung continuum) were in 9749 Topic 19 outcome (n) but are not in 9478 - the Quantum Physics topic now covers wavefunctions and particle-in-a-box instead. Semiconductor and laser content is H3-level enrichment, not in H2 9478.
16 Nuclear Physics and Radioactivity
Isotopes: same proton number, different neutron number. Nucleon: proton or neutron. Nuclide: specified by Z and N.
Binding energyEb: energy to separate nucleus into nucleons; mass defectΔm: Eb=Δmc2. Stability: larger Eb/A usually means more stable. Energy release in fission and fusion: products lie at higher Eb/A.
Radioactivity: spontaneous and random decay; emissions α, β, γ.
α: He nucleus, strongly ionising, weakly penetrating.
Rutherford scattering inference: atom mostly empty space, small dense positive nucleus.
Hazards: depend on penetrating ability, ionising effect, and half-life. α ionises strongly but stops in skin or paper (dangerous if inhaled or ingested); β penetrates a few millimetres of tissue (aluminium or thick plastic shielding adequate); γ penetrates deeply (lead or concrete shielding required). Long half-lives extend contamination risk. Reduce dose by minimising exposure time, maximising distance, and using appropriate shielding. Background radiation: all non-sample sources, including cosmic rays, terrestrial radionuclides (e.g. radon), medical procedures, and trace nuclear-industry contributions.
