IB Physics HL Paper 2: How to Write Long Answers That Score

IB Physics HL Paper 2 lasts 2 hours 30 minutes, carries 90 marks and is worth 44% of the final grade. These figures come from the IB Physics guide for first assessment 2025 and match the cover of the May 2025 HL Paper 2. The paper mixes short calculations with extended responses, and because the current syllabus (taught from 2023, first examined in 2025) removed Paper 3, Paper 2 is now the only place where an HL student has to explain physics in full sentences.

Why this changes your preparation.

Under the old syllabus, data analysis and the option topic sat in Paper 3, and many students treated written answers as a minor skill. Now the written marks are concentrated in one paper, alongside calculations on all five themes: space, time and motion; the particulate nature of matter; wave behaviour; fields; nuclear and quantum physics.

What Paper 1 already covers.

Paper 1 is split into 1A (multiple choice) and 1B (data based questions on a practical context). If you want the technique for graphs, uncertainties and unfamiliar data, read my guide to IB Physics Paper 1B data based questions. This article deals only with the extended answers of Paper 2.

What the examiner rewards.

A Paper 2 question worth 3 to 6 marks with the command word explain, describe, outline or suggest is marked against a list of separate marking points. Each point is a single physical idea. The length of your answer earns nothing on its own; the points you make explicit earn everything.

The command word in an IB Physics Paper 2 question tells you exactly how many links the examiner expects. State wants a fact with no reasoning, outline wants a brief account, describe wants a detailed account of what happens, explain adds the causes, and suggest asks for a plausible physical reason in a context you have not seen.

Read the command word and the mark together.

The marks in square brackets are your best guide to length. An explain question worth [2] usually needs a cause and its effect; the same command word worth [5] needs a chain of five connected steps, each one named. Students who write the same three lines for both lose marks on the second.

Describe is not explain.

If a question asks you to describe the motion of a charged particle in a uniform magnetic field, the marks go to what happens: circular path, constant speed, plane perpendicular to the field. If it asks you to explain the same motion, the marks go to why: the force $F = qvB$ acts perpendicular to the velocity, so it does no work and provides the centripetal force.

Suggest rewards physics, not guessing.

A suggest question has no single right answer, but every acceptable answer names a mechanism. Write the quantity involved and the direction of its effect, for example that a larger resistance reduces the induced current and therefore the braking force.

A 5 mark answer in IB Physics Paper 2 differs from a 2 mark answer by the number of explicit steps, not by length. The strong answer names each physical quantity in turn (flux, emf, current, force, net force) and gives each one its own sentence, so every marking point can be ticked separately.

The question.

Here is a typical HL Paper 2 style item on induction: a bar magnet is released from rest above a long vertical copper tube and falls through it. Explain why the magnet reaches a terminal velocity. [5]

The answer that scores 2.

"The magnet induces a current in the tube. This current slows the magnet down until it falls at a constant speed." This earns the idea of an induced current and, generously, the idea of opposition. It never mentions flux, never states why the force grows, and never says what terminal velocity means in terms of forces.

The answer that scores 5.

Written as a chain, one point per sentence:

• As the magnet falls, the magnetic flux through each section of the tube changes.
• By Faraday's law an emf is induced, and because copper is a conductor, eddy currents flow in the tube.
• By Lenz's law these currents produce a magnetic field that opposes the change in flux, so there is an upward magnetic force on the magnet.
• As the speed increases, the rate of change of flux increases, so the emf, the current and the upward force all increase.
• Terminal velocity is reached when the upward magnetic force equals the weight, so the net force and the acceleration are zero.

Why the difference is in the steps.

Count the physical quantities: the weak answer names one (current), the strong one names flux, emf, current, force, speed, weight and acceleration. The fourth sentence is the one most students skip, yet without it there is no reason for the speed to stop increasing. That missing link is where most extended answers in IB Physics lose their marks.

Using the law, not just its name.

You can support the second sentence with $\varepsilon = -N\frac{\Delta \Phi}{\Delta t}$, but the equation alone is not an explanation. The mark goes to the sentence that connects it to this situation.

IB Physics HL Paper 2 covers the whole syllabus, and many explain questions sit on themes shared with SL, such as energy, waves and thermal physics. The HL extensions are where the chains get longest: gravitational and electric fields (D.1 and D.2), motion in electromagnetic fields (D.3), electromagnetic induction (D.4) and quantum physics (E.2). These topics are conceptual, so they lend themselves to explain questions as much as to calculations.

Fields.

Typical prompts ask why the work done moving a charge along an equipotential is zero, or why escape speed does not depend on the mass of the escaping object. The chain always runs through potential, potential energy and work, with each step named. Writing "because it is an equipotential" without saying that $\Delta V = 0$ and therefore $W = q\Delta V = 0$ usually earns one mark out of two.

Induction.

Beyond falling magnets, expect generators, transformers and eddy current braking. The same four links recur: change of flux, induced emf, induced current, opposing effect. Practise saying which quantity changes and why before reaching for Lenz's law.

Quantum physics.

The classic question asks why light below the threshold frequency ejects no electrons, however intense it is. The chain: light arrives as photons of energy $E = hf$; each electron absorbs the energy of one photon; if $hf$ is less than the work function, no electron escapes; increasing intensity increases the number of photons per second, not the energy of each photon. Four quantities, four marks.

How this fits HL versus SL.

SL students meet fields and quantum ideas in a lighter form, and the HL extensions are where the longest chains appear. If you are still deciding on the level, my comparison of IB Physics HL and SL sets out the extra content.

IB Physics HL Paper 2 gives you 150 minutes for 90 marks, which is about 1 minute 40 seconds per mark. A 5 mark explain question therefore deserves around 8 minutes, including the time to plan the chain. If the final number is wrong, only the working you wrote down can still earn marks, so write every step.

Use the reading time.

IB exams normally begin with 5 minutes of reading time in which you may not write; the instructions on the cover of your paper confirm it. Spend it locating the explain and suggest items and deciding which topic chains you will need, so the planning is already done when the pen goes down.

Plan in keywords, write in sentences.

For a long answer, jot the quantities in the margin in order (flux, emf, current, force, net force), then turn each into one sentence. This takes under a minute and stops you writing a paragraph that circles around the same idea.

Show that questions are free method marks.

When a question says show that $v \approx 3.2\ \text{m s}^{-1}$, the marks are for the working, so write the equation, the substitution with units and a final value to one more significant figure than the one given. If you get stuck, use the given value in the next part: mark schemes apply error carried forward (ECF), so later marks remain available.

Never leave an explain blank.

A partial chain earns partial credit. If time is running out, write the first two links (what changes, what is induced) in two short sentences; that alone often secures two marks that a blank space never will.

Practise on real papers.

Work on past and specimen papers under timed conditions and mark them with the official mark scheme, point by point. My guide on where to find IB past papers explains what is available for the new syllabus.

A student who has IB Physics Paper 2 long answers under control can explain a physics idea out loud in short, numbered steps, naming a quantity at each step, and can say how many marks each step would earn. Long answers that still score low on explain questions mean the steps are missing, not the knowledge.

Simple checks at home.

Ask your child to explain one phenomenon from their notes (why a satellite stays in orbit, why a transformer needs alternating current) in four sentences. Then ask which physical quantity each sentence is about. Hesitation here is a reliable sign that the chains are not yet automatic.

How to support them.

Encourage timed practice on real questions with the official mark scheme, rather than rereading notes. Praise answers that are short and complete, not long ones. If the gap persists into the final year, a few targeted sessions focused on the HL topics with the longest cause and effect chains usually make a visible difference.