A-level and IB · Sciences

A-level Physics: core concepts

A-level Physics flashcards on particles, quantum ideas, mechanics, materials, waves, circuits, fields, thermal physics and radioactivity, with worked numbers.

40 cards7 topicsAbout 15 minutes a roundUK A-level Physics, comparable to Grade 12 physics plus parts of first-year university mechanics, waves and electricity

Independent study material written by StudyBrix, not produced or reviewed by any exam board or by the International Baccalaureate Organization. Check your own specification or subject guide.

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About this deck

This deck reviews the physics that most A-level courses in England share: measurement and uncertainty, particles and photons, mechanics and materials, waves and optics, electric circuits and capacitors, circular motion and oscillations, gravitational, electric and magnetic fields, thermal physics and the ideal gas, and nuclear decay and binding energy. It helps students revising for final papers and Canadian students who want to check readiness for first-year university physics.

AQA, Edexcel and OCR cover the same core but differ in options (for example astrophysics or medical physics), equation sheets and the order of topics. Check your board's specification and data and formulae sheet so you know which equations are given and which you must recall.

You should be fluent with GCSE physics, rearranging equations, standard form and basic trigonometry. Work each example with units at every line, then check significant figures. For field and circuit cards, draw the diagram first; many lost marks come from a missing direction or a wrong sign convention.

Common mistakes: forgetting to convert eV to J (multiply by 1.60 * 10^-19), using diameter instead of radius, mixing up the gradient and the area of a graph, and treating gravitational potential as positive. With capacitors and decay, remember that after one time constant about 37% remains, not 50%.

Before you start: GCSE physics and maths (or Grade 11 physics and pre-calculus): equations of motion, energy, basic circuits and trigonometry.

All 40 cards

Cover the definitions with a sheet of paper and test yourself, or use the study modes above.

Measurements, particles and quanta

Percentage uncertainty: Absolute uncertainty divided by the measured value, times 100. When quantities are multiplied, add percentages; for a power, multiply by the power.Example: Side 2.50 +/- 0.01 m is 0.4%; the area of a square with that side has 0.8% uncertainty.
SI base units: The seven base units are kg, m, s, A, K, mol and cd; all other units are built from them.Example: The newton is kg m s^-2 because F = ma.
Specific charge: Charge of a particle divided by its mass, in C/kg.Example: Proton: 1.60 * 10^-19/1.67 * 10^-27 = 9.58 * 10^7 C/kg.
Photon energy: Light comes in packets with energy E = hf = hc/lambda.Example: Light of 500 nm: E = 6.63 * 10^-34 * 3.00 * 10^8/5.00 * 10^-7 = 3.98 * 10^-19 J, about 2.49 eV.
Photoelectric effect: Electrons are emitted from a metal only if each photon has at least the work function energy: hf = phi + maximum kinetic energy.Example: Bright red light may emit nothing while dim ultraviolet emits electrons, because photon energy depends on frequency.
de Broglie wavelength: Any moving particle has a wavelength lambda = h/p, where p is momentum.Example: Electron at 1.0 * 10^6 m/s: 6.63 * 10^-34/(9.11 * 10^-31 * 1.0 * 10^6) = 7.3 * 10^-10 m, similar to atomic spacing.
Quark composition of hadrons: Baryons are three quarks, mesons are a quark and an antiquark. Up quarks have charge +2/3 and down quarks -1/3.Example: Proton uud: 2/3 + 2/3 - 1/3 = +1. Neutron udd: 0.

Mechanics and materials

Power and velocity: Power is the rate of doing work; for a constant force moving at speed v, P = Fv.Example: A car's driving force of 500 N at 20 m/s delivers 10 kW.
Conservation of momentum: In a closed system with no external force, total momentum before an interaction equals total momentum after.Example: 2 kg at 3 m/s hits a 1 kg mass at rest and they stick: v = 6/3 = 2 m/s.
Impulse: Force times the time it acts, equal to the change in momentum; it is the area under a force-time graph.Example: A 0.15 kg ball going from +20 to -20 m/s has a momentum change of 6 kg m/s.
Young modulus: Tensile stress divided by tensile strain for a material obeying Hooke's law; a measure of stiffness.Example: Wire 2.0 m long, 1.0 * 10^-6 m^2 area, 50 N, extends 0.50 mm: stress 5.0 * 10^7 Pa, strain 2.5 * 10^-4, so E = 2.0 * 10^11 Pa.
Elastic strain energy: Energy stored in a stretched material, equal to the area under its force-extension graph: Fx/2 within the limit of proportionality.Example: A spring stretched 0.10 m by 40 N stores 2.0 J.

Waves

Stationary wave: Formed when two waves of the same frequency travel in opposite directions and superpose, giving fixed nodes and antinodes.Example: Fundamental on a 0.80 m string: wavelength 1.6 m. With wave speed 240 m/s, f = 150 Hz.
Diffraction grating equation: d sin theta = n lambda, where d is the slit spacing and n the order.Example: 300 lines per mm gives d = 3.33 * 10^-6 m. For 600 nm, first order sin theta = 0.18, theta = 10.4 degrees.
Young's double slit: Fringe spacing w = lambda D/s, where D is the slit-to-screen distance and s the slit separation.Example: 600 nm, D = 2.0 m, s = 0.50 mm: w = 2.4 mm.
Critical angle: The angle of incidence in the denser medium at which the refracted ray travels along the boundary; sin c = n2/n1.Example: Glass (1.5) to air: sin c = 1/1.5, so c = 41.8 degrees. Larger angles give total internal reflection.
Path difference and interference: Constructive interference when the path difference is a whole number of wavelengths; destructive when it is an odd number of half wavelengths, for coherent sources in phase.Example: Two speakers in phase, wavelength 0.40 m: a path difference of 0.20 m gives a quiet spot.

Electricity

Resistivity: A property of a material: rho = RA/L, in ohm metres. Resistance of a wire is R = rho L/A.Example: Copper (1.7 * 10^-8 ohm m), 2.0 m long, 0.50 mm^2 area: R = 1.7 * 10^-8 * 2.0/(0.50 * 10^-6) = 0.068 ohms.
Resistors in parallel: The reciprocal of the total resistance is the sum of the reciprocals; the total is always less than the smallest branch.Example: 6 ohms and 3 ohms in parallel: 1/6 + 1/3 = 1/2, so the total is 2 ohms.
Internal resistance: The resistance inside a source, so terminal potential difference falls as current rises: E = I(R + r).Example: E = 12 V, r = 0.5 ohm, R = 5.5 ohm: I = 2.0 A and terminal pd = 11 V.
Potential divider: Two resistors in series share the supply voltage in proportion to their resistances: V(out) = V(in) R2/(R1 + R2).Example: 9.0 V across 1 kilohm and 2 kilohm: 6.0 V across the 2 kilohm resistor.
Capacitor discharge: Charge falls exponentially: Q = Q0 e^(-t/RC). The time constant RC is the time to fall to about 37%.Example: 100 kilohm and 47 microfarads: RC = 4.7 s. After 4.7 s, 37% of the charge remains.
Energy stored in a capacitor: Equal to the area under a charge-voltage graph: E = QV/2 = CV^2/2.Example: 470 microfarads at 12 V stores 0.5 * 470 * 10^-6 * 144 = 0.034 J.

Motion in circles and oscillations

Centripetal acceleration: Acceleration toward the centre of a circular path, a = v^2/r = omega^2 r, needed to keep changing the direction of motion.Example: A car at 15 m/s on a bend of radius 50 m: a = 225/50 = 4.5 m/s^2.
Simple harmonic motion: Oscillation where acceleration is proportional to displacement and directed toward equilibrium: a = -omega^2 x.Example: A 1.0 m simple pendulum has T = 2 pi sqrt(1.0/9.81), about 2.0 s.
Resonance: Large-amplitude oscillation when the driving frequency equals the natural frequency of a system; damping lowers and broadens the peak.Example: Soldiers break step on bridges so their marching frequency cannot drive the structure at its natural frequency.

Fields

Gravitational field strength: Force per unit mass at a point; around a spherical mass, g = GM/r^2.Example: At Earth's surface: 6.67 * 10^-11 * 5.97 * 10^24/(6.37 * 10^6)^2 = 9.81 N/kg.
Gravitational potential: Work done per unit mass to bring a mass from infinity to a point; V = -GM/r, always negative.Example: At Earth's surface V is about -6.25 * 10^7 J/kg.
Coulomb's law: The force between point charges is F = kQq/r^2 with k = 8.99 * 10^9 N m^2 C^-2; like charges repel.Example: Two 1.0 microcoulomb charges 0.10 m apart: F = 8.99 * 10^9 * 10^-12/0.010 = 0.90 N.
Uniform electric field: Between parallel plates the field strength is constant: E = V/d.Example: 500 V across plates 2.0 cm apart gives 25000 V/m.
Force on a current-carrying wire: A wire at right angles to a magnetic field feels F = BIL; Fleming's left-hand rule gives the direction.Example: B = 0.20 T, I = 3.0 A, L = 0.50 m: F = 0.30 N.
Charged particle in a magnetic field: The force BQv is always at right angles to the velocity, so the particle moves in a circle of radius r = mv/(BQ).Example: Electron at 2.0 * 10^6 m/s in 0.010 T: r = 9.11 * 10^-31 * 2.0 * 10^6/(0.010 * 1.60 * 10^-19), about 1.1 mm.
Faraday's and Lenz's laws: Induced emf equals the rate of change of flux linkage; its direction opposes the change that caused it.Example: A magnet pushed into a coil induces a current whose field repels the approaching pole.
Ideal transformer: The voltage ratio equals the turns ratio, Vs/Vp = Ns/Np, and with no losses input power equals output power.Example: 230 V on 1000 primary turns with 50 secondary turns gives 11.5 V.

Thermal and nuclear physics

Specific heat capacity: The energy needed to raise 1 kg of a substance by 1 K: Q = mc delta theta.Example: Heating 0.50 kg of water by 20 K takes 0.50 * 4180 * 20 = 41800 J.
Specific latent heat: Energy per kilogram to change state at constant temperature: Q = mL.Example: Melting 0.20 kg of ice (L = 334 kJ/kg) takes 66.8 kJ.
Mean kinetic energy of gas molecules: For an ideal gas, the average translational kinetic energy per molecule is (3/2)kT, so it depends only on absolute temperature.Example: At 300 K: 1.5 * 1.38 * 10^-23 * 300 = 6.2 * 10^-21 J.
Radioactive decay constant: The probability per unit time that a nucleus decays; it links to half-life by lambda = ln 2/half-life, and A = lambda N.Example: After three half-lives, 1/8 of the original nuclei remain: 8 g of a sample becomes 1 g.
Alpha, beta and gamma radiation: Alpha (helium nuclei) is strongly ionizing and stopped by paper; beta (electrons) by a few mm of aluminium; gamma (photons) is reduced by thick lead.Example: Smoke alarms use alpha sources because the short range keeps the radiation inside the device.
Mass defect and binding energy: The mass of a nucleus is less than its separate nucleons; the missing mass times c^2 is the energy that would be needed to pull it apart. 1 u corresponds to 931.5 MeV.Example: Helium-4: mass defect about 0.0304 u, so binding energy is about 28.3 MeV, or 7.1 MeV per nucleon.