IB Physics SL & HL · Exam Technique
IB Physics Long Answer Questions: A Smarter Strategy for Higher Marks
Learn how to read command terms, build a chain of reasoning, set out equations and match your answer to the marks available, so your written Physics earns what your understanding deserves.
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Many students who sit at a 4 or 5 in IB Physics do not have a concept problem. They have an answer-writing problem. They know the physics, but the page shows an unexplained equation, a bare number, a vague phrase like "it gets bigger", or a diagram with no labels. Examiners can only reward what is written, so reasoning that stays in your head earns nothing.
IB Physics Long Answer Questions reward a visible chain: the principle, the relationship, the working and the link to the conclusion. This guide shows how to build that chain, how to respond to each command term and how much to write for the marks on offer. It is practical teaching advice, not an official IB specification. Always check your current subject guide and past markschemes.
What Are IB Physics Long Answer Questions?
"Long answer" is not an official category. Students use it for any question needing more than a one-line result: explanation questions, extended response questions, structured multi-part questions and calculations that also need justification. The depth required depends on the wording and the marks available, not on a fixed rule for each command term.
- Explain / justify / suggest: give reasons, linking cause to effect.
- Describe / compare / distinguish: state features, similarities or differences precisely.
- Discuss / evaluate: weigh more than one point and reach a supported judgement.
- Predict: give an outcome, often with a reason.
- Show that / derive: reach a given result with every step visible.
- Calculate and explain: numerical work plus a physics statement.
The International Baccalaureate publishes the official subject guide and command term definitions. Use those as your authority and treat this page as a technique guide on top.
The Biggest Problem: Knowing Physics but Not Showing It
Here are original examples of the same understanding, written weakly and then clearly.
The stronger answers name the physical quantity, state the mechanism and finish by linking back to the question. That is a chain of reasoning, and it is what most markschemes are built to reward.
7 Powerful Strategies for IB Physics Long Answer Questions
1. Start With the Command Term
The verb tells you what kind of answer earns marks. Students lose marks by describing when asked to explain, or stating when asked to justify.
Example: "Explain why the gas cools" needs a mechanism, not "it cools down".
- Circle the command term before reading further.
- Ask: am I giving features, reasons or a judgement?
Common mistake: restating the question as the answer.
2. Identify the Physics Principle
Name the idea in play: conservation of momentum, Newton's second law, energy transfer, Snell's law. Marks are often tied to applying the correct principle.
Example: "Momentum is conserved because there is no external resultant force in the collision."
- Write the principle in a short phrase first.
- Check its conditions actually apply.
Common mistake: using energy conservation for an inelastic collision without accounting for losses.
3. Build a Clear Chain of Reasoning
Each sentence should lead to the next. Use linking words such as "therefore", "so" and "because" to show cause and effect.
Example: Larger mass → smaller acceleration for the same force → smaller change in velocity in the same time.
- Aim for cause, mechanism, effect.
- Do not skip the middle step.
Common mistake: jumping from cause straight to effect.
4. Show Equations and Substitution Clearly
A correct number with no working can lose method marks if it is wrong, and may lose marks even when right on show-that or multi-step questions.
Example: F = ma → a = 12 / 3.0 = 4.0 m s⁻²
- Write the relationship, then substitute, then answer.
- Define any symbol you introduce.
Common mistake: an unexplained equation dropped onto the page.
5. Use Correct Physics Terminology
Precise language shows understanding. "Speed" and "velocity", "heat" and "internal energy", "force" and "pressure" are not interchangeable.
Example: "The frequency of collisions with the wall increases" is stronger than "more collisions happen".
- Keep a personal glossary of terms you often misuse.
- Replace "it", "stuff" and "bigger" with named quantities.
Common mistake: writing "heat" when internal energy or temperature is meant.
6. Check Units, Signs, Directions and Significant Figures
Small slips cost marks across a whole paper. Vectors need direction, and final answers should usually reflect the precision of the data given.
Example: "Displacement is 4.2 m to the left" rather than "4.2".
- State a sign convention for one-dimensional motion.
- Give a final answer to a sensible number of significant figures.
Common mistake: forgetting to convert cm to m or km h⁻¹ to m s⁻¹.
7. Match the Depth of Your Answer to the Marks
The marks suggest how many distinct points are expected. Use them as a guide, not a rigid word count.
Example: A 2-mark "explain" often needs two linked ideas. A 1-mark question rarely needs a paragraph.
- Count the marks, then plan that many separate points.
- Stop once you have answered the question.
Common mistake: writing everything you know instead of what was asked.
How to Structure a Long IB Physics Answer
You do not need every stage every time. A pure "state" question needs one. A calculation needs equation, working and unit. An explanation needs idea, principle and reasoning. A "show that" needs all the working and a final statement of the given value.
Under-answering means stopping after the first correct step. Over-writing means repeating textbook content that does not answer the question. Both are fixed by planning one line per expected mark.
Mark-Based Approach
| Marks | Practical approach |
|---|---|
| 1 mark | One precise point or result |
| 2 marks | Two relevant points, or a result plus justification |
| 3 marks | Clear explanation with linked reasoning |
| 4+ marks | Structured multi-step explanation or reasoning |
The exact marking approach depends on the question and markscheme. Marks should not be treated as a rigid word-count rule.
IB Physics Command Terms: What Each One Asks For
These are practical interpretations. Confirm official definitions in your IB subject guide.
| Term | What to do | Weak response | Stronger response |
|---|---|---|---|
| Calculate | Find a numerical answer with working | Number only | Equation, substitution, answer with unit |
| Determine | Reach an answer, possibly from data or a graph | Guessing from the graph | Method shown, values read clearly, unit given |
| Describe | State features or sequence of events | Vague, incomplete | Accurate, precise statements of what happens |
| Explain | Give reasons or mechanism | Restates the observation | Principle plus linked cause and effect |
| Compare | Give similarities and differences | Describes each separately | Direct, point-by-point comparison |
| Distinguish | Make clear the difference | Defines only one item | Both items with the key difference stated |
| Discuss | Offer a balanced set of points | One-sided list | Several developed points, sensible conclusion |
| Evaluate | Weigh strengths and limitations | Lists points, no judgement | Points weighed against evidence, judgement made |
| Justify | Give valid reasons for an answer | Assertion | Claim backed by principle or calculation |
| Predict | Give an expected outcome | Outcome with no basis | Outcome with brief physics reason |
| Suggest | Propose a plausible idea | Irrelevant idea | Sensible proposal linked to the context |
| Show that | Reach the given result | Jumps to the answer | Every step, an extra-precision value, final statement |
Common IB Physics Long-Answer Mistakes (and Fixes)
| Mistake | Correction |
|---|---|
| 1. Defining instead of explaining | Apply the definition to the situation given. |
| 2. Equation with no physics | Say why the relationship applies here. |
| 3. Final number with no working | Show equation, substitution and answer. |
| 4. Ignoring units | Write units at every final answer. |
| 5. Vague words ("bigger", "faster") | Name the quantity and the direction of change. |
| 6. No cause and effect | Use "because", "so", "therefore" deliberately. |
| 7. Ignoring sign or direction | Set a convention and state vector directions. |
| 8. Writing everything you know | Plan one point per mark and stop. |
| 9. Not answering the command term | Underline it and check your last sentence against it. |
| 10. Wrong terminology | Keep a glossary of confused pairs. |
| 11. Missing diagram | Sketch labelled forces, rays or circuits when helpful. |
| 12. Stopping after the first step | Check whether the marks demand a further link. |
| 13. Copying the question wording | Add new information, not a restatement. |
| 14. Unsupported conclusion | Tie it back to your evidence or calculation. |
How to Use the Markscheme Properly
A markscheme is a diagnostic tool, not an answer bank to memorise. After attempting a question under timed conditions:
- Identify the required ideas, one per mark.
- Notice the terminology that is accepted and compare it with yours.
- Mark yourself honestly and spot missing reasoning steps.
- Record each lost mark in an error log: topic, type of error, what to do next time.
- Reattempt a similar question a few days later.
Never copy wording blindly. The goal is to understand why each point earns credit so you can build it yourself in a new context.
Original Practice Questions for Long Answers
These are original practice questions created for Nivara Academy. They are not IB questions and have no official markscheme.
| Question | Marks | Examiner looks for / structure | Common mistake |
|---|---|---|---|
| Explain why a gas in a sealed rigid container exerts a greater pressure when heated. | 3 | Higher kinetic energy → more frequent, harder collisions → greater pressure at constant volume. | Stops at "particles move faster". |
| A 2.0 kg trolley moving at 3.0 m s⁻¹ sticks to a stationary 1.0 kg trolley. Calculate the common speed and state whether kinetic energy is conserved. | 4 | Momentum conservation, substitution, answer with unit, compare kinetic energy before and after. | Assumes energy is conserved. |
| Explain why a car moving at constant speed round a circular track is accelerating. | 2 | Velocity is a vector, its direction changes → acceleration towards the centre. | Talks about speed only. |
| Describe and explain what happens to the brightness of a lamp when a second identical lamp is added in parallel to a cell with negligible internal resistance. | 3 | Same potential difference across each lamp, so same current in each, so brightness unchanged. Total current from the cell increases. | Claims brightness decreases. |
| Evaluate whether a student's experiment with a single timing of a falling ball gives a reliable value of g. | 3 | Random error and reaction time, repeat readings, reasoned judgement. | Lists errors with no judgement. |
Long Answer Checklist
Before moving on, ask:
- Did I answer the command term?
- Did I identify the correct Physics principle?
- Did I show important working?
- Did I explain the reasoning?
- Did I use correct Physics terminology?
- Did I include units where needed?
- Did I check significant figures where appropriate?
- Did I answer every part of the question?
- Does my conclusion actually answer the question?
How Nivara Academy Can Help
Some IB Physics students do not need more content. They need to see where marks are being lost and practise fixing it. That usually means work on exam technique, written explanations, problem-solving, long-answer practice, structured revision and individual feedback on real answers.
Nivara Academy is a personalised 1-to-1 IB learning and support platform. There is no pressure to commit. Discuss Your IB Physics Goals or Explore 1-to-1 IB Physics Support.
Book an IB Physics ConsultationIB Physics Long Answer Questions: FAQ
How do I answer IB Physics long answer questions?
Read the command term, name the principle, write the relationship, show working, link reasoning to the question and finish with a clear statement and unit.
How long should an IB Physics long-answer response be?
There is no fixed length. Plan roughly one distinct point per mark and stop when the question is fully answered.
How can I score more marks on IB Physics explanation questions?
Replace vague wording with named quantities, and link each step with cause and effect.
How should I approach a 4-mark IB Physics question?
Expect several linked points or steps. Sketch a quick plan, such as principle, equation, working, reasoning, and check each against the marks.
What is the difference between "describe" and "explain" in IB Physics?
Describe states what happens or the features. Explain gives the reasons why, using physics principles.
Should I show all working in IB Physics?
Show the equation, substitution and key steps. Skip trivial arithmetic but never present a multi-step result without method.
How can I improve my Physics written answers?
Rewrite weak answers, compare them with markscheme ideas, keep an error log and practise under timed conditions.
Why do I lose marks even when my final answer is correct?
Marks are often awarded for method, reasoning, units or a required statement. A correct number alone may not show these.
How can I use IB Physics markschemes for practice?
Mark your own answer, find missing ideas and terminology, log the error, then reattempt a similar question later. Do not memorise wording.
Can a tutor help me improve IB Physics long-answer questions?
A tutor can give feedback on your actual written answers and show where marks are lost. Results depend on practice and effort, and no outcome is guaranteed.
About This Guide
Prepared by the academic team at Nivara Academy with a focus on practical IB Physics learning and exam preparation. It is an independent study resource and is not an official IB publication.