IB Group 4 · Sciences
Physics
2025 syllabus · First assessment 2025
Five themes built on the guide’s understandings. Each note is tied to exactly what the syllabus says you must understand — with the SL core and Additional HL content clearly split.
A. Theme A: Space, time and motion
Classical mechanics: describing and predicting motion, the forces that cause it, momentum, energy and power, plus the HL extensions into rigid-body rotation and special relativity.
A.1 — Kinematics
Describing motion — Position, velocity and acceleration; displacement vs distance; instantaneous vs average values.
The equations of motion — The four SUVAT equations for uniformly accelerated motion, and uniform vs non-uniform acceleration.
Projectile motion — Resolving motion into horizontal and vertical components, and the qualitative effect of fluid resistance.
A.2 — Forces and momentum
Newton’s laws and free-body diagrams — The three laws, forces as interactions, free-body diagrams, resultant force, equilibrium and force pairs.
Contact forces — Normal force, friction (static and dynamic), tension, the elastic restoring force (Hooke’s law), viscous drag and buoyancy.
Field forces — The gravitational (weight), electric and magnetic forces that act at a distance.
Momentum, impulse and collisions — Linear momentum and its conservation, impulse, the two forms of Newton’s second law, and elastic/inelastic collisions and explosions.
Circular motion — Centripetal acceleration and force, and the link between angular velocity and linear speed.
A.3 — Work, energy and power
Work and the conservation of energy — Conservation of energy, work as energy transfer, Sankey diagrams, and W = Fs cos θ.
Mechanical energy — Kinetic, gravitational potential and elastic potential energy, and conservation of mechanical energy.
Power, efficiency and energy density — Power as the rate of energy transfer, efficiency, and the energy density of fuel sources.
A.4 — Rigid body mechanics
Torque and rotational equilibrium — Torque of a force about an axis, its sense, and the condition for rotational equilibrium.
Rotational kinematics — Angular displacement, velocity and acceleration, and the equations of motion for uniform angular acceleration.
Moment of inertia and Newton’s second law for rotation — How mass distribution sets the moment of inertia, and τ = Iα.
Angular momentum and rotational energy — Angular momentum and its conservation, angular impulse, rotational kinetic energy, and rolling without slipping.
A.5 — Galilean and special relativity
Reference frames and Galilean relativity — Inertial reference frames, the Galilean transformation and velocity addition.
The postulates and Lorentz transformations — The two postulates of special relativity, the Lorentz transformations, γ, and relativistic velocity addition.
Space–time interval, proper time and length — The invariant space–time interval, and the meaning of proper time and proper length.
Time dilation and length contraction — Δt = γΔt₀, L = L₀/γ, the relativity of simultaneity, and muon-decay evidence.
Space–time diagrams — Constructing and reading space–time diagrams, world lines, and tan θ = v/c.
B. Theme B: The particulate nature of matter
Thermal physics and electricity: the molecular model of matter, heat transfer, the greenhouse effect, the gas laws, electric current and circuits, plus the HL extension into thermodynamics and entropy.
B.1 — Thermal energy transfers
Molecular theory, temperature and internal energy — The molecular model, density, the Kelvin and Celsius scales, average kinetic energy, and internal energy.
Heat, phase change and latent heat — Phase changes at constant temperature, and quantitative heat transfer with specific heat capacity and latent heat.
Mechanisms of thermal energy transfer — Conduction, convection and thermal radiation, including the rate of conduction and the Stefan–Boltzmann law.
Black-body radiation and stars — The black-body emission spectrum, Wien’s displacement law, luminosity and apparent brightness.
B.2 — Greenhouse effect
Energy balance: emissivity, albedo and the solar constant — Conservation of energy for the Earth–atmosphere system, emissivity, albedo, the solar constant and equilibrium temperature.
Greenhouse gases and the enhanced greenhouse effect — The main greenhouse gases, how they absorb and re-emit infrared radiation, and the enhanced greenhouse effect.
B.3 — Gas laws
Pressure, moles and the ideal gas law — Pressure, amount of substance, the ideal-gas model, the empirical gas laws and the ideal gas equation.
Kinetic theory and the internal energy of a gas — Pressure from molecular collisions, the internal energy of a monatomic ideal gas, and when the ideal-gas model holds.
B.4 — Thermodynamics
The first law of thermodynamics — Q = ΔU + W as conservation of energy for a closed system, work done, and the sign convention.
Entropy and the second law — Entropy as disorder, its macroscopic and statistical definitions, and the second law.
Thermodynamic processes — Isovolumetric, isobaric, isothermal and adiabatic processes on a P–V diagram.
Heat engines and the Carnot cycle — Cyclic processes, heat-engine efficiency, and the Carnot limit.
B.5 — Current and circuits
Charge, current and potential difference — Cells and emf, current as a flow of charge, potential difference, and conductors vs insulators.
Resistance, Ohm’s law and power — Resistance and resistivity, Ohm’s law, ohmic vs non-ohmic behaviour, and electrical power.
Series, parallel and internal resistance — Combining resistors in series and parallel, emf with internal resistance, and variable resistors.
C. Theme C: Wave behaviour
Oscillations and waves: simple harmonic motion, the wave model, reflection/refraction/interference, standing waves and resonance, and the Doppler effect, with the HL extensions into SHM algebra, diffraction and Doppler equations.
C.1 — Simple harmonic motion
Defining SHM — The conditions for SHM, the defining equation a = −ω²x, and the quantities that describe an oscillation.
The period of oscillating systems — The period of a mass–spring system and a simple pendulum, and the energy changes over a cycle.
SHM equations and energy — Phase angle, the displacement/velocity equations, and the quantitative energy of an oscillation.
C.2 — Wave model
Describing waves — Transverse and longitudinal waves, the wave equation v = fλ, and energy transfer by a wave.
Sound and electromagnetic waves — The nature of sound and electromagnetic waves, the EM spectrum, and mechanical vs EM waves.
C.3 — Wave phenomena
Reflection, refraction and diffraction — Wavefronts and rays, wave behaviour at boundaries, and diffraction around bodies and apertures.
Snell’s law and total internal reflection — Refraction with Snell’s law, the critical angle and total internal reflection.
Interference and Young’s double slit — Superposition, coherent sources, the interference conditions, and the double-slit equation.
Single-slit diffraction and gratings — Single-slit diffraction and intensity, its modulation of the double-slit pattern, and diffraction gratings.
C.4 — Standing waves and resonance
Standing waves: nodes and antinodes — How standing waves form by superposition, and the nodes, antinodes, amplitude and phase along them.
Harmonics in strings and pipes — Standing-wave patterns for the boundary conditions of strings and pipes, and the nth harmonic.
Resonance and damping — Natural frequency and driving frequency, light/critical/heavy damping, and the effects of resonance.
C.5 — Doppler effect
The Doppler effect — The Doppler effect for sound and light, wavefront diagrams, the light shift, and spectral-line evidence.
Doppler equations for sound — The observed-frequency equations for a moving source and a moving observer.
D. Theme D: Fields
Gravitational, electric and magnetic fields: field strength and field lines, the motion of charges in fields, with the HL extensions into potential and potential energy, orbits, and electromagnetic induction.
D.1 — Gravitational fields
Newton’s gravitation and Kepler’s laws — Kepler’s three laws and Newton’s universal law of gravitation for point masses.
Gravitational field strength — Gravitational field strength as force per unit mass, and gravitational field lines.
Gravitational potential and potential energy — Gravitational potential energy, potential, the potential gradient, and equipotential surfaces.
Orbits, escape and orbital speed — Escape speed, orbital speed, satellite energetics, and the effect of atmospheric drag.
D.2 — Electric and magnetic fields
Electric charge and Coulomb’s law — Charge, Coulomb’s law, charge conservation, Millikan’s experiment and methods of charging.
Electric fields — Electric field strength, field lines, field-line density, and the uniform field between parallel plates.
Magnetic fields — Magnetic field lines for magnets, wires, coils and solenoids, and the field direction from a current.
Electric potential and potential energy — Electric potential energy, potential, the potential gradient, work done, and equipotentials.
D.3 — Motion in electromagnetic fields
Charged particles in fields — The motion of a charged particle in uniform electric, magnetic, and crossed E and B fields.
Force on charges and currents — The force on a moving charge (F = qvB sin θ) and on a current-carrying conductor (F = BIL sin θ).
Parallel wires and charge-to-mass ratio — The force between parallel current-carrying wires, and finding a particle’s charge-to-mass ratio.
D.4 — Induction
Magnetic flux and Faraday’s law — Magnetic flux, and the emf induced by a changing flux (Faraday’s law).
Motional emf and Lenz’s law — The emf induced in a moving conductor, and the direction of induced emf from Lenz’s law.
Generators and self-induction — The sinusoidal emf of a rotating coil, the effect of rotation frequency, and self-induction.
E. Theme E: Nuclear and quantum physics
The atom and its nucleus: atomic structure and spectra, radioactive decay, fission, and fusion in stars, with the HL extensions into the Bohr model, quantum physics (photoelectric effect, matter waves, Compton scattering) and the exponential decay law.
E.1 — Structure of the atom
The nuclear atom and spectra — The Rutherford experiment, nuclear notation, atomic energy levels and emission/absorption spectra.
Nuclear radius and scattering — The nuclear-radius relation and density, and deviations from Rutherford scattering.
The Bohr model — Discrete hydrogen energy levels from the quantization of angular momentum.
E.2 — Quantum physics
The photoelectric effect — The photoelectric effect as evidence for the particle nature of light, and Einstein’s equation.
The wave nature of matter — Particle diffraction, wave–particle duality and the de Broglie wavelength.
Compton scattering — Compton scattering as further evidence of the particle nature of light.
E.3 — Radioactive decay
Binding energy and mass–energy — Isotopes, mass defect and binding energy, the binding-energy curve, E = mc² and the strong force.
Alpha, beta and gamma decay — The random nature of decay, the three decay types, decay equations, neutrinos, and penetration.
Activity and half-life — Activity, count rate and half-life, decay over integer half-lives, and background radiation.
The exponential decay law — The decay constant, the exponential decay law, activity, and the half-life relation.
Nuclear stability and evidence — The neutron-to-proton ratio, the binding-energy curve, and evidence for nuclear energy levels and the neutrino.
E.4 — Fission
Nuclear fission and chain reactions — Energy released in fission, and the role of chain reactions.
Nuclear reactors and waste — The role of control rods, moderators, heat exchangers and shielding, and managing fission products.
E.5 — Fusion and stars
Fusion in stars — Stellar equilibrium, fusion as a star’s energy source, the conditions for it, and stellar evolution.
The Hertzsprung–Russell diagram — The main regions of the HR diagram and the properties of stars in each.
Measuring stars — Stellar parallax and distance units, and determining stellar radii from luminosity and temperature.
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