Not all IB Physics topics are equal. Some come up constantly in the exams. Others are lighter, or tested in more predictable ways. Knowing which is which changes how you allocate your revision time.
This is the Pareto Principle in action: 80% of your exam marks come from roughly 20% of your effort, if that effort is pointed in the right direction. The question is how to figure out where to point it.
The topics that get the most teaching time are the topics that get the most exam marks.
How to Identify the High-Priority Topics
Ideally you would analyse every past paper, count how many marks each topic gets, and build a weighting table. With an established syllabus, that works well.
With the current IB Physics syllabus (first examined 2025), there simply are not enough past papers yet to run that analysis reliably.
The next best proxy is teaching hours. The IB allocates specific hours to each topic, and those allocations directly signal how much the examiners expect students to know. More hours means more content, which means more marks available.
The total is 150 hours for SL and 240 hours for HL. Here is how those hours break down across the five themes:
| Theme | SL hours | HL hours |
|---|---|---|
| A: Space, time and motion | 27 | 42 |
| B: The particulate nature of matter | 24 | 32 |
| C: Wave behaviour | 17 | 29 |
| D: Fields | 19 | 38 |
| E: Nuclear and quantum physics | 23 | 39 |
| Scientific Investigation | 30 | 30 |
| Individual study | 10 | 30 |
The Scientific Investigation hours explain why the IA counts for 20% of your final grade. It is a substantial time commitment that the IB has built directly into the course structure.
Key Topics: Standard Level
Theme A: Space, time and motion (27 hours)
The most heavily weighted SL theme. Within it, A.2 Forces and Momentum is the standout priority. It is conceptually rich, mathematically demanding, and appears repeatedly across Paper 1A and Paper 2. Master it thoroughly.
The rest of Theme A (A.1 Kinematics, A.3 Work, Energy and Power) is also high priority and tends to reward students who can apply equations to unfamiliar scenarios.
Theme D: Fields (19 hours)
D.2 Electric and Magnetic Fields carries significant weight and is one of the topics most likely to appear in multi-step Paper 2 questions. It requires genuine understanding, not just memorisation.
Theme E: Nuclear and Quantum Physics (23 hours)
Focus on E.3 Radioactive Decay and E.5 Fusion and Stars. Key calculations include mass-energy equivalence, luminosity, Wien’s displacement law, and the Stefan-Boltzmann law. These come up reliably and are very learnable with practice.
Theme B: The Particulate Nature of Matter (24 hours)
A wide theme that can feel scattered. B.5 Current and Circuits gets significant teaching time due to practical work, but is not always a heavy exam focus. B.2 The Greenhouse Effect is worth knowing well. It tends to produce predictable, accessible questions.
Theme C: Wave Behaviour (17 hours)
The lightest theme by hours, but do not underestimate it. Standing waves and double-slit diffraction appear regularly in longer Paper 2 questions. Examiners like them because they test both conceptual understanding and calculation in the same question.
Key Topics: Higher Level
The teaching hour gaps at HL are more pronounced, which makes prioritisation even more important.
Theme A: Space, time and motion (42 hours)
A.2 Forces and Momentum is as critical at HL as it is at SL, but the questions are harder, often requiring multi-step problem solving with difficult command words like explain and determine.
A.4 Rigid Body Mechanics and A.5 Galilean and Special Relativity are HL-only additions. Their teaching hour allocation is not the highest, but in the early years of a new syllabus, examiners tend to test the new topics prominently. Do not leave these as afterthoughts.
Theme D: Fields (38 hours)
The biggest jump from SL to HL is in Theme D. Gravitational, electric, and magnetic fields all get substantially more depth at HL, and D.4 Induction is added as an HL-only topic. This is the theme where HL students most need to invest serious revision time.
Theme E: Nuclear and Quantum Physics (39 hours)
At HL, E.1 Structure of the Atom, E.2 Quantum Physics, and E.3 Radioactive Decay are all high priority. Quantum physics demands precision: the photoelectric effect, wave-particle duality, and quantum energy levels all require careful, exact explanation in the exam.
Theme C: Wave Behaviour (29 hours)
More depth is expected at HL, particularly in analysing interference patterns, diffraction, and complex wave phenomena. Practise interpreting and explaining wave behaviour in exam conditions, not just recalling definitions.
The Scientific Investigation
Regardless of SL or HL, your Scientific Investigation counts for 20% of your final grade. That is 20% that does not depend on what comes up in the exam. It is entirely within your control, and it rewards students who approach it methodically.
If you are still in the planning stages of your IA, the complete IB Physics Scientific Investigation guide covers everything from research question to evaluation.
How to Use This
Knowing the priority topics is step one. Step two is knowing how to study them effectively. For the full method, read how to study IB Physics.
For a breakdown of how the exam itself is structured (which papers, how many marks, what types of questions), see the IB Physics exam breakdown.
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Sally Weatherly is a Fellow of the Institute of Physics, author of 4 IB Physics books (two hit #1 on Amazon), and has been teaching IB Physics since 2004. GradePod has helped 30,000+ students since 2020.