What Are the Most Common Mistakes in IB Physics Exams?

The biggest culprits are missing units, wrong significant figures, misreading command terms like "show that" or "derive", and skipping working on calculation questions. According to the IB Physics guide (first exams 2025), Paper 2 marks are awarded for method as much as final answers — so blank working loses marks even with a correct number.

Paper 1 (the multiple-choice paper, now including some data-based questions) catches students who rush and don't eliminate answers systematically. The classic mistake is picking an answer that has the right numbers but wrong units or wrong order of magnitude — examiners deliberately build these as distractors.

On Paper 2, the recurring error is answering the question you expected rather than the one actually asked — especially on "explain" versus "calculate" parts within the same sub-question. Students also frequently forget to state the physical principle (e.g. conservation of energy) before doing the maths, which costs the reasoning mark even when the arithmetic is right.

Slow down on unit conversions before you touch the calculator — that's where most careless errors start, not in the algebra. Write intermediate values with units at every step rather than only at the end; it forces you to catch a wrong conversion before it propagates through the rest of the answer.

Examiners award a specific mark for correct units on final numerical answers — leave it off and you lose that mark even with the right number. The mistake I see most is students writing the unit only in their working and forgetting to carry it through to the boxed final answer.

"Show that" gives you the final answer already and asks you to prove it using full working — examiners want every step, not a jump from question to answer. Skipping steps here is the single most common way students lose marks on questions where the answer is essentially handed to them.

Match the significant figures in your final answer to the least precise piece of data given in the question — usually 2 or 3 sig figs for IB Physics. Rounding too early in a multi-step calculation, rather than only at the final answer, is the mistake that most often produces a slightly-wrong result.

The most common IA mistake is a research question that's too vague to generate meaningful data, followed closely by weak uncertainty analysis — students often quote an uncertainty without explaining where it came from. Under the current IA criteria, Analysis and Evaluation reward genuine engagement with error sources, not just a stated percentage.

Always check whether a graph question wants the gradient of the raw data or the gradient after a linearisation — plotting the wrong variables against each other is the classic trap. Draw the best-fit line properly too; markers penalise a line forced through the origin when the data doesn't support it.

Past paper practice under timed conditions, marked against the actual mark scheme, closes the gap between knowing the content and scoring on the day. Most students plateau not because they don't understand the physics, but because they've never seen how examiners actually allocate the marks on a real question.

SL students most often lose marks on basic unit and sig fig slips because the questions are shorter and leave less room to recover. HL students more often lose marks on multi-step derivations and the option topics, where one wrong substitution early on cascades through several following marks.

This is one of the most common things parents ask me, and the answer is almost always exam technique, not understanding — missing units, wrong significant figures, or misreading a command term like "determine" versus "show that". These are fixable within weeks through structured past-paper practice, not a sign your child needs to relearn the content.

Topical worksheets that isolate one skill at a time — unit conversions, data analysis, command-term practice — work better than repeatedly attempting full past papers before the basics are solid. On RevisionPrep, the Topical Worksheets and Mock Papers are built around exactly these recurring examiner-flagged error types, alongside Revision Notes for the content itself.