Q: What does H2 Physics in A-Level: Definitions and Formulae Guide cover? A: Concise definitions and core formulae for A-Level H2 Physics, cleaned and typeset for quick revision with inline and block KaTeX.
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.
Uncertainties: absolute Δx, fractional Δx/x
, percentage
(Δx/x)×100%
.
Propagation
Sums or differences: Δy≈Δa+Δb if y=a±b.
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: static Fs≤μsN, kinetic Fk=μkN. 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
Pressure: P=F/A. Hydrostatic pressure (incompressible, at rest): p=ρgh. Upthrust: U=ρgVdisplaced. Flotation: floating body has U=W.
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 6.02 x 10^23.
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: potentiometer preferred to voltmeter (zero current draw avoids terminal drop).
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.
Wave-particle duality: de Broglie wavelength λ=h/p=h/(mv). Uncertainty principle: ΔxΔp≥ℏ/2, ΔEΔt≥ℏ/2.
Atomic energy levels: discrete bound energies; excitation by inelastic collisions or photon absorption; emission/absorption spectra from transitions. X-rays: characteristic lines from inner-shell transitions, plus continuous bremsstrahlung spectrum; minimum wavelength when one electron loses all KE in a single event.
Semiconductors and lasers (high level): intrinsic vs extrinsic, p-n junctions (diodes, LEDs, photodiodes); lasers need population inversion, gain medium, pumping, optical cavity.
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.
