IGCSE Physics Formula Sheet – All Key Equations (Cambridge 0625)
Every key formula for Cambridge IGCSE Physics 0625, organised by topic so you can learn them in the same order as the syllabus. Unlike some exam boards, Cambridge does NOT provide an equation sheet in the exam – you are expected to memorise all of these, so treat this page as your complete memorisation list and work through it a section at a time.
Motion
| Formula | What it means / When to use it |
|---|
| average speed v = s / t | Speed = distance travelled divided by time taken. Use for any journey where the speed is not constant. |
| acceleration a = (v − u) / t | Acceleration = change in velocity divided by time taken, where u is the initial velocity and v is the final velocity. |
| distance travelled = area under a speed-time graph | On a speed-time graph, count or calculate the area between the line and the time axis to find the total distance. |
| velocity is speed in a stated direction | Velocity is a vector: it has size and direction. Two objects can have the same speed but different velocities if they travel in different directions. |
Forces and Mass
| Formula | What it means / When to use it |
|---|
| resultant force F = ma | A resultant (unbalanced) force causes acceleration: force (N) = mass (kg) × acceleration (m/s2). |
| weight W = mg | Weight is the gravitational force on a mass: weight (N) = mass (kg) × gravitational field strength g (N/kg). |
| density ρ = m / V | Density = mass divided by volume. Use it to identify materials or to find the mass of a known volume. |
| moment = F × perpendicular distance from the pivot | The turning effect of a force. Use the distance measured at right angles from the pivot to the line of the force. |
| Hooke’s law: F = kx | For a spring stretched within its limit of proportionality, the force is proportional to the extension x; k is the spring constant. |
| resultant force = vector sum of all forces | Add forces in the same direction and subtract forces in opposite directions. A zero resultant means constant velocity (or rest). |
| pressure p = F / A | Pressure = force divided by the area over which it acts. A smaller area gives a larger pressure for the same force. |
| liquid pressure p = ρgh | Pressure at a depth h in a liquid of density ρ. It increases with depth and does not depend on the shape of the container. |
Energy, Work and Power
| Formula | What it means / When to use it |
|---|
| work done W = Fd | Work = force × distance moved in the direction of the force. Work done equals the energy transferred, in joules. |
| kinetic energy KE = 0.5mv2 | The energy of a moving object: half × mass × (speed)2. Note the speed is squared, so doubling speed quadruples KE. |
| gravitational potential energy GPE = mgh | Energy stored when an object is raised through a height h against gravity. |
| power P = W / t (also P = E / t) | Power = work done (or energy transferred) divided by time. The unit is the watt: 1 W = 1 J/s. |
| efficiency = (useful energy output / total energy input) × 100% | Shows what fraction of the input energy is transferred usefully. Can also be written with useful power output over total power input. |
| energy is conserved, never created or destroyed | In any transfer, the total energy stays the same; “wasted” energy is usually transferred to the surroundings as thermal energy. |
Waves, Light and Sound
| Formula | What it means / When to use it |
|---|
| wave speed v = fλ | Wave speed = frequency × wavelength. Applies to all waves, including light and sound. |
| frequency f = 1 / T | Frequency (Hz) is one divided by the period T, the time for one complete wave. |
| law of reflection: angle of incidence = angle of reflection | Both angles are measured from the normal, the line at right angles to the surface at the point where the ray meets it. |
| refractive index n = sin i / sin r | For light entering a medium from air or a vacuum: n = sin(angle of incidence) / sin(angle of refraction). |
| critical angle: sin c = 1 / n | Beyond the critical angle, light inside the medium is totally internally reflected instead of refracting out. |
| speed of light in a vacuum = 3.0 × 108 m/s | A constant to remember: all electromagnetic waves travel at this speed in a vacuum (and almost the same in air). |
Electricity and Magnetism
| Formula | What it means / When to use it |
|---|
| charge Q = It | Charge (coulombs) = current (amps) × time (seconds). |
| voltage V = IR | Voltage = current × resistance. Rearrange to find any one of V, I or R when you know the other two. |
| electrical power P = VI (= I2R = V2/R) | Power transferred by a component. Use whichever form matches the values given in the question. |
| electrical energy E = VIt | Energy transferred = voltage × current × time (combines E = VQ with Q = It). |
| resistors in series: R = R1 + R2 + … | In a series circuit the total resistance is the sum of the individual resistances, and the current is the same everywhere. |
| resistors in parallel: 1/R = 1/R1 + 1/R2 | Adding resistors in parallel reduces the total resistance; the voltage across each branch is the same. |
| transformer: Vp/Vs = Np/Ns | The ratio of voltages on the primary and secondary coils equals the ratio of their turns. Step-up transformers have more secondary turns. |
| ideal transformer: Pp = Ps, so VpIp = VsIs | For a 100% efficient transformer, the power out equals the power in, so stepping voltage up means stepping current down. |
| electromagnetic induction: a voltage is induced when a conductor cuts magnetic field lines | The generator effect. The induced voltage increases with faster movement, a stronger magnet or more turns on the coil. |
| motor effect force F = BIl (Supplement) | Force on a current-carrying conductor in a magnetic field = flux density × current × length of conductor in the field. |
Thermal Physics
| Formula | What it means / When to use it |
|---|
| thermal energy E = mcΔθ | Energy needed to change temperature: mass × specific heat capacity × temperature change. |
| latent heat energy E = mL | Energy for a change of state at constant temperature: mass × specific latent heat (fusion or vaporisation). |
| Boyle’s law: pV = constant | For a fixed mass of gas at constant temperature, pressure × volume stays the same: p1V1 = p2V2. |
| pressure law: p / T = constant (Supplement) | For a fixed mass of gas at constant volume, pressure is proportional to temperature in kelvin, so p1/T1 = p2/T2. |
Atomic Physics
| Formula | What it means / When to use it |
|---|
| half-life = time for the activity (or number of undecayed nuclei) to halve | Find it from a decay curve by reading the time taken for the count rate to fall to half its value; it is the same at any point on the curve. |
| fraction remaining after n half-lives = (1/2)n | Multiply the starting activity or mass by (1/2) once for each half-life that passes: after 3 half-lives, 1/8 remains. |
| corrected count rate = measured count rate − background count rate | Always subtract the background radiation count, measured with no source present, before using count-rate data in half-life work. |
Constants to Remember
g = 9.8 N/kg on Earth (0625 often takes g = 10 N/kg in questions – use the value the question gives).
Speed of light in a vacuum: 3.0 × 108 m/s.
Speed of sound in air: approximately 340 m/s.
Keep Revising
Head back to the Physics MCQs hub for practice questions, and memorise the equations for the other boards too:
This is an original revision aid prepared by QuaidianPoint. It is not affiliated with Cambridge Assessment International Education.
Cambridge IGCSE Physics (0625) – Practice MCQs by Section
Free practice questions for every section of the syllabus – 30 MCQs with answers and explanations on each page.
Unit 1 – General Physics
Unit 2 – Thermal Physics
Unit 3 – Waves, Light and Sound
Unit 4 – Electricity and Magnetism
Unit 5 – Atomic Physics
Unit 6 – Space Physics
