IGCSE Physics Equations List
Most Physics calculation marks are method marks, awarded for writing the correct equation and substituting into it. Recalling the equation is therefore worth a mark even when the arithmetic goes wrong.
Some equations are printed on the Physics paper and some must be recalled, and the split differs between papers. This sheet gathers every equation the 0625 syllabus uses, grouped by topic, with each symbol and its unit. Learn the whole list and the distinction stops mattering.
Motion, forces and energy
| Quantity | Equation | Units |
|---|---|---|
| Speed | speed = distance divided by time | m/s |
| Acceleration | a = change in velocity divided by time | m/s2 |
| Density | density = mass divided by volume | kg/m3 or g/cm3 |
| Resultant force | F = ma | N |
| Weight | W = mg | N |
| Momentum | p = mv | kg m/s |
| Impulse | F t = change in momentum | N s |
| Moment | moment = force x perpendicular distance | N m |
| Work done | W = F d | J |
| Kinetic energy | E = half m v2 | J |
| Change in potential energy | change in E = m g change in h | J |
| Power | P = work done divided by time | W |
| Efficiency | useful output divided by total input | no unit, or per cent |
| Hooke's law | F = k x | N |
| Pressure | p = F divided by A | Pa |
| Pressure in a liquid | p = rho g h | Pa |
Thermal physics and waves
| Quantity | Equation | Units |
|---|---|---|
| Thermal energy | E = m c change in temperature | J |
| Wave speed | v = f x wavelength | m/s |
| Frequency and period | f = 1 divided by T | Hz |
| Refractive index | n = sin i divided by sin r | no unit |
| Refractive index from speed | n = speed in vacuum divided by speed in medium | no unit |
| Critical angle | sin c = 1 divided by n | degrees |
Electricity, magnetism and space
| Quantity | Equation | Units |
|---|---|---|
| Current | I = Q divided by t | A |
| Potential difference | V = W divided by Q | V |
| Resistance | R = V divided by I | ohm |
| Resistors in series | R total = R1 + R2 | ohm |
| Resistors in parallel | 1 over R total = 1 over R1 + 1 over R2 | ohm |
| Electrical power | P = I V, or P = I2 R | W |
| Electrical energy | E = I V t | J |
| Transformer | Vp divided by Vs = Np divided by Ns | no unit |
| Orbital speed | v = 2 pi r divided by T | m/s |
How to use this sheet
- Write the equation, then the substitution, then the answer with a unit, on three separate lines. Each line can carry a mark.
- Check the unit of your answer against the equation. If the units do not work out, the rearrangement is wrong.
- Convert everything to SI units before substituting. Centimetres, grams and minutes cause more lost marks than any misremembered formula.
- Learn which quantities are vectors, since those cannot simply be added.
- Round to the same number of significant figures as the data, normally two or three.
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Frequently asked questions
Which IGCSE Physics equations do I have to memorise?
Cambridge prints some equations on the paper and expects others to be recalled, and the split differs between papers and syllabus versions. The safest approach is to learn the whole list, then whatever is printed becomes a bonus rather than a dependency.
Why should I write the equation before substituting?
Most Physics calculation questions award a method mark for the correct equation and another for correct substitution, separately from the answer mark. Writing both lines means an arithmetic slip costs one mark rather than all of them.
What is the most common unit error?
Failing to convert before substituting. Grams must become kilograms, centimetres must become metres, and minutes must become seconds. Areas are worse still, since one square metre is ten thousand square centimetres, not one hundred.
How do I know if I have rearranged an equation correctly?
Check the units. If you are calculating a speed and your units come out as metres multiplied by seconds rather than metres per second, the rearrangement is inverted. This catches most errors before the arithmetic is even done.
Practise the topics this sheet supports
Other reference sheets
Written to the published Cambridge IGCSE syllabuses. Always check the formula list and data sheet issued with your own paper, since the material provided differs between subjects and syllabus versions. Last reviewed 2026-08-12.