IGCSE · 8 June 2026 · 4 min read
The IGCSE physics equations you must know by heart
Updated 25 September 2026
Watch a student lose a calculation question and you will usually see the same failure: not the arithmetic, not the physics — the first ten seconds, when the right equation should have appeared and did not.
There is no single universal IGCSE equation list: Cambridge and Edexcel routes differ, and requirements can change by exam year. Use the current specification to establish what you need, including any equations provided in the exam.
The equation families
Start with motion, forces, energy, thermal physics, waves and electricity, then check the remaining topics for your board. Space physics may add orbital-speed, redshift or Hubble calculations. This grouping helps organise practice; it does not replace a complete syllabus checklist.
Group them as families, not as a flat list. The brain stores connected structures far better than isolated lines — and half the equations are one rearrangement away from each other.
Memorize with units attached
Never learn an equation without its units. Units are the built-in error detector of physics: if your answer's units are wrong, your equation was wrong, and you can catch it in the exam. Students who master units also stop fearing the 'show that' questions, because they can verify each step.
Tariq in Dubai learned the memory techniques in my course and says he has not forgotten a single equation since. The method is unglamorous: write the full set from memory once a week, mark your gaps, repeat. Permanence comes from retrieval, not from re-reading.
Units are the built-in error detector of physics.
From recall to marks
Recall is the entry ticket; the marks come from the routine that follows. Write the equation, substitute with units, solve, and sanity-check the size of the answer. Four steps, every time, no shortcuts — this is the routine that stops students losing marks on calculations they know how to do, which is where most IGCSE physics grades are actually decided.
Questions, explained
Choose a question for a direct answer, then explore the explanation and supporting resources. Each answer has its own link to save or share.
How do I choose an equation when the question looks unfamiliar?
Identify the quantity requested, list the known quantities with units, and describe the physical situation before choosing an equation. Check whether its conditions apply. If one equation does not connect the known and unknown quantities, look for an intermediate quantity that links two relationships.
Suppose a 12 V motor draws 2.0 A for 30 s, and you need its electrical energy input. First calculate input power: P = VI = 24 W. Then use E = Pt = 24 × 30 = 720 J. The intermediate quantity is power. You can combine the equations as E = VIt, but writing the two stages makes the reasoning easier to check and helps prevent confusion with useful mechanical output.
If my units are correct, does that prove my Physics equation is correct?
No. Matching units is a necessary consistency check, but it cannot detect every error. A missing numerical factor or an equation applied outside its conditions may still give the correct units. Check the physical relationship, assumptions and numerical result as well.
Both mv² and ½mv² have units of joules, but the kinetic energy of a non-relativistic object is ½mv². Likewise, dividing a total distance by a time gives speed units even if you used the wrong time interval. Use units to catch a class of mistakes, then inspect factors, powers, signs and the information taken from the question. A sensible estimate of magnitude provides a further check.
How do I rearrange an equation when the unknown is squared?
Isolate the squared quantity before taking a square root, keeping the whole expression inside the root. For E = ½mv², multiply by 2 and divide by m to obtain v² = 2E/m, then v = √(2E/m) for the non-negative speed.
If E = 50 J and m = 4.0 kg, v = √(100/4.0) = 5.0 m/s. Taking √100 and then dividing by 4.0 would give the wrong answer because the mass also belongs inside the root. Check your rearrangement by substituting the result into the original equation: ½ × 4.0 × 5.0² = 50 J. Reverse substitution is a useful check when you are unsure about an algebraic step.
Sources and specifications
- Cambridge IGCSE Physics 0625 syllabus, 2026–2028
- Pearson Edexcel International GCSE Physics: specification and assessment materials
- Cambridge published marking principles, including scientific meaning and alternative wording
- Pearson Edexcel 4PH1 Paper 2P mark scheme, June 2023: marking guidance and accepted alternatives