Cambridge IGCSE / A-Level
IGCSE Physics 0625 Paper 4: Structure, Question Styles and Technique
Paper 4 is the Extended theory paper for IGCSE Physics 0625: 1 hour 15 minutes, 80 marks, 50 percent of the qualification. It covers all six syllabus topics with structured questions mixing definitions, calculations and explanations. Motion, forces and energy plus electricity and magnetism usually carry the largest share of marks.
Physics Paper 4 was the exam I was most nervous about, because knowing the formula is maybe a third of each calculation mark and the rest is setup, substitution and units. I sit Cambridge IGCSE myself, and the difference between my early practice scores and my later ones was almost entirely technique rather than extra physics. These notes cover the structure of Paper 4, the topics that dominate it, three original exam-style questions solved with full working, and the specific habits, like rearranging in symbols before substituting, that reliably convert understanding into marks.
How Paper 4 is structured
Paper 4 runs 1 hour 15 minutes for 80 marks and counts for 50 percent of the qualification. The Extended route pairs it with Paper 2, multiple choice at 30 percent, and Paper 5 or 6 for practical skills at 20 percent. The paper is a run of structured questions, usually around 9 to 11 of them, each anchored in one topic but happy to pull in another: a motion question can end in an energy calculation, and a circuits question can finish with magnetism. All six syllabus areas appear: motion, forces and energy; thermal physics; waves; electricity and magnetism; nuclear physics; and space physics. There is no formula sheet, so every equation on the syllabus has to be memorised, and a good chunk of marks each session are effectively free if you can recall, rearrange and substitute correctly with units. Space physics is the newest section of the syllabus and examiners use it regularly, including Supplement-only ideas like redshift and orbital speed.
Topic weighting: where the marks sit
Motion, forces and energy is the biggest topic in the syllabus and it behaves that way in Paper 4, often spanning two or three questions: motion graphs, resultant force, momentum, moments, work, power and efficiency. Electricity and magnetism is the second pillar, with circuit analysis, resistance calculations, electromagnetic induction and transformers appearing in some form nearly every session. Waves gives reliable marks through the wave equation, refraction and refractive index, and the electromagnetic spectrum. Thermal physics leans on specific heat capacity calculations and particle explanations. Nuclear physics questions are usually shorter: decay equations, half-life from data, and uses of isotopes. Space physics rounds out the paper with orbits, the life cycle of stars and redshift. My practical takeaway from past papers: momentum, specific heat capacity and transformers are the three calculation types I drilled hardest, because they reappear constantly and each has a classic trap, which is direction, unit conversion and the ideal transformer assumption respectively.
Question styles and command words
Cambridge physics questions climb in a predictable way. Parts begin with state or define, worth 1 mark, where the syllabus definition word for word is the safest answer. Describe and explain parts want the mechanism: for thermal questions that means particles, spacing and energy transfer; for induction it means field lines being cut and an induced e.m.f. Calculations dominate the middle of each question, and Cambridge marks them in stages: correct equation, correct substitution, correct answer with unit. Writing the symbol equation first is not decoration, it is usually the first mark. Show that questions give you the answer and ask for the route, so show every step and quote your final value to more significant figures than the value given. Graph parts want labelled axes, sensible scales and a best fit line. The 4 to 6 mark extended explanations are credited as separate points, so short separate sentences beat paragraphs. Suggest means apply known physics to an unfamiliar setup, and sensible attempts score.
Technique that actually moves your score
Units and rearrangement are where I lost marks early on. Now I rearrange in symbols before substituting numbers, and I convert units before anything else: grams to kilograms, centimetres to metres, minutes to seconds. Second habit: significant figures. I keep the full calculator value through multi-step calculations and round only the final answer, usually to 3 significant figures. Third: direction. Momentum and force questions on Extended expect a stated direction, and defining one direction as positive at the start of the working prevents sign chaos. Fourth: graphs. Gradient and area have physical meanings, the gradient of a distance-time graph is speed and the area under a speed-time graph is distance, and Paper 4 asks you to extract one of them nearly every session. Finally, timing: 80 marks in 75 minutes means the big calculations cannot each eat five minutes. If a part stalls, I write the equation and the substitution for partial credit, move on, and come back at the end.
Worked questions, step by step
A trolley of mass 2.0 kg moving at 3.0 m/s collides with a stationary trolley of mass 1.0 kg. The trolleys stick together and move off in the same direction. (a) Calculate the velocity of the trolleys immediately after the collision. (b) State whether the collision is elastic or inelastic and justify your answer with a calculation. [6]
- (a) Total momentum before = (2.0 x 3.0) + (1.0 x 0) = 6.0 kg m/s.
- Momentum is conserved, so after the collision: 6.0 = (2.0 + 1.0) x v.
- v = 6.0 / 3.0 = 2.0 m/s in the original direction of the moving trolley.
- (b) KE before = 1/2 x 2.0 x 3.0^2 = 9.0 J. KE after = 1/2 x 3.0 x 2.0^2 = 6.0 J.
- Kinetic energy falls from 9.0 J to 6.0 J, so the collision is inelastic. Momentum is conserved but kinetic energy is not.
Answer: (a) 2.0 m/s in the original direction. (b) Inelastic: kinetic energy falls from 9.0 J to 6.0 J.
Where marks slip: State conservation of momentum explicitly and give the direction of the final velocity. In part (b) the mark is for comparing the two kinetic energy values, not just for the word inelastic.
Try one yourself: Rerun the numbers with the second trolley moving at 1.0 m/s towards the first. Choosing a positive direction before you start is what keeps the signs honest.
A transformer connects a 240 V mains supply to a 12 V lamp rated at 24 W. The primary coil has 4000 turns. (a) Calculate the number of turns on the secondary coil. (b) Assuming the transformer is 100 percent efficient, calculate the current in the primary coil. (c) Explain why a transformer only works with alternating current. [7]
- (a) Use Vp / Vs = Np / Ns: 240 / 12 = 4000 / Ns.
- Ns = 4000 x 12 / 240 = 200 turns.
- (b) For 100 percent efficiency, power in = power out, so Ip x Vp = 24 W.
- Ip = 24 / 240 = 0.10 A.
- (c) Alternating current in the primary produces a continuously changing magnetic field in the core.
- This changing field links the secondary coil and induces an e.m.f. in it. With direct current the field is constant, no field lines are cut, so no e.m.f. is induced.
Answer: (a) 200 turns. (b) 0.10 A. (c) A.c. gives a changing magnetic field in the core, which induces an e.m.f. in the secondary; d.c. gives a constant field, so nothing is induced.
Where marks slip: Part (c) is a classic 3 marker: changing field, field linking or cutting the secondary coil, e.m.f. induced. The word changing is the single most important word in the answer.
Try one yourself: Try a step-up version: a power station transformer raising 25 kV to 400 kV for transmission. Then explain, using P = I^2 R, why transmitting at high voltage reduces power loss in the cables.
An electric heater rated at 50 W heats a 0.50 kg aluminium block for 4.0 minutes. The temperature of the block rises from 20 degrees C to 45 degrees C. (a) Calculate the energy supplied by the heater. (b) Use the data to calculate a value for the specific heat capacity of aluminium. (c) The accepted value is 900 J/(kg degrees C). Explain why the experimental value is higher. [6]
- (a) Convert the time first: 4.0 minutes = 240 s. Then E = P x t = 50 x 240 = 12000 J.
- (b) The equation is E = m x c x (change in temperature), rearranged to c = E / (m x change in temperature).
- Temperature change = 45 - 20 = 25 degrees C.
- c = 12000 / (0.50 x 25) = 960 J/(kg degrees C).
- (c) Some of the electrical energy is transferred to the surroundings and the apparatus, not the block, so the energy absorbed by the aluminium is less than 12000 J.
- The calculation assumes all 12000 J entered the block, so it divides too large an energy by the true temperature rise, which inflates the value of c.
Answer: (a) 12000 J. (b) 960 J/(kg degrees C). (c) Thermal energy is lost to the surroundings, so less than 12000 J actually heats the block; using the full 12000 J makes the calculated value too big.
Where marks slip: The minutes to seconds conversion is a whole mark in disguise: miss it and parts (a) and (b) both fall. For (c), name where the energy went and link it to the effect on the calculated value.
Try one yourself: Invert it: given c = 900 J/(kg degrees C), a 0.25 kg block and a 60 W heater, find how long it takes to raise the temperature by 30 degrees C if 20 percent of the energy is lost.
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Solve my question →Quiz me on this topicQuestions students ask
How long is Physics 0625 Paper 4 and how many marks is it worth?
It is 80 marks in 1 hour 15 minutes, and it is 50 percent of the IGCSE. You sit it with Paper 2, the multiple choice paper worth 30 percent, and a practical paper worth 20 percent.
Is there a formula sheet for IGCSE Physics 0625?
No. Every equation on the syllabus must be memorised, including Supplement-only ones like orbital speed. I keep a single sheet of every equation and rewrite it from memory once a week until the blanks disappear.
Does Paper 4 include space physics?
Yes, regularly. Orbits, the Sun as a star, stellar life cycles and redshift are all fair game, and several parts of the topic are Supplement-only, which concentrates them on Paper 4 rather than the Core paper.
What are the hardest parts of Paper 4?
For most people it is multi-step calculations that cross topics, explain questions where the scheme wants precise mechanism words, and anything involving unit conversions or directions. All three improve with drills rather than more content revision.