7 IB Physics Option A exam mistakes to avoid

If you’ve found your way here, you’re likely looking for tips and hints for your IB Physics Option A Relativity exam. Congrats, you’re in the right place! If you are taking a different Physics Option, visit our IB Physics page for further resources and articles to help you with your study and revision.

Below are seven mistakes IB students commonly make on the IB Physics Option A exam. We hope you find them useful. This advice was taken from our study guide Physics Option A: Relativity Standard and Higher Level by Hugh Duncan, which is packed full of top tips, worked examples, and practice questions (see our article 10 IB Physics Option A questions you should know for examples) to help you prepare and revise.

IB Physics Option A Relativity common exam errors

1. Forgetting units. Remember, when velocity is asked for, it is often as a fraction of the speed of light, e.g. 0.5c or a percentage, e.g. 50% the speed of light, or with units, e.g. 1.5 x 10⁸ ms^-1. It is particularly important when dealing with the units for mass-energy and momentum. Remember, students are expected to use MeVc^-2 for mass-energy and MeVc^-1 for momentum. Similarly on space-time graphs, it is usual to label the time axis as ct to bring the units in line with the distant units of light years.

2. Not rounding answers. Remember the rounding rules, when multiplication or division occur the final answer has no more significant figures than the least number of figures given in the question. Many points are lost, especially on paper three so be vigilant.

3. Incomplete answers. Definitions are often asked and students should learn the full standard wording of each. For example, when asking for the light postulate of relativity, there might be one or two points. Whichever it is, students must state that all observers measure the same speed for light in a vacuum.

4. Not showing your work. Sometimes there are several points for a numerical answer and marks are awarded for showing certain steps. A student might get the final answer wrong but could earn as much as 3 points out of 4 if the intermediate steps are correct and shown and 75% could still earn a 7 on the IB scale! Isn’t that a good incentive?!

5. Confusing rest frame with moving frame. This mistake happens when an observer is watching something move past at close to the speed of light, such as spacecraft. The student associates themselves with the ‘observer' and considers themselves at rest. But if something is happening on a moving spacecraft, such as a mass, length or time event, m₀, L₀ and t₀, such things are at rest relative to the moving spacecraft. What the observer sees is m, L and t, as they are in relative motion with the spacecraft.

6. Forgetting signs in relative velocity problems. Remember velocity is a vector quantity so direction is important and if one direction is taken as positive, the opposite is negative.

7. Drawing diagrams free hand in pen. Clarity is important in exam answers and diagrams should be drawn with a sharp pencil and ruler, though labelling should be done in pen.

---

Continue your IB Physics Relativity revision

The tips offered above are quick wins you can implement during your IB exams to ensure you don't miss out on any valuable marks. If you've come across this article as a DP1 student that's great. Take the advice above and start implementing it now. If you do, by the time your IB Physics exam comes around you'll be well placed to do your best.

You can discover more helpful tips, in-depth syllabus review, and lots of practice questions in our Physics Option A: Relativity Standard and Higher Level study guide. Be sure to also check out our IB Physics subject page for additional free resources including helpful articles, study tools, and more.