IB Physics Fields (HL) questions become much more manageable once you recognize their recurring structures. Most ask you to interpret a field, connect force and potential, analyse a particle or satellite, or apply electromagnetic induction. The most effective method is to attempt a question independently, identify the precise step where your reasoning failed, and then watch a worked solution that models the complete process.
This guide explains the current syllabus coverage, the question formats you should expect, the calculations that repeatedly appear, and the mistakes that cost marks. It is aligned with the IB Physics course first assessed in 2025, in which Fields is Theme D rather than the separate Topic 10 used in the previous syllabus.
Where Fields appears in IB Physics HL
The current course divides Theme D into four topics:
| Topic | Main content | HL status |
|---|---|---|
| D.1 Gravitational fields | Gravitation, field strength, orbital motion, potential, energy and escape speed | Shared topic with additional HL content |
| D.2 Electric and magnetic fields | Coulomb force, field strength, field lines, potential and equipotentials | Shared topic with additional HL content |
| D.3 Motion in electromagnetic fields | Forces on charges and conductors, circular particle motion and field selection | Studied at SL and HL |
| D.4 Induction | Magnetic flux, Faraday's law, Lenz's law and motional emf | HL only |
The official IB Physics subject brief allocates 38 recommended syllabus hours to Fields at HL, compared with 19 at SL. These are recommended teaching hours, not a statement that Fields will occupy a fixed proportion of an examination.
At HL, Paper 1 lasts 2 hours and contributes 36% of the final grade. It contains Paper 1A multiple-choice questions and Paper 1B data-based questions. Paper 2 lasts 2 hours 30 minutes, contributes 44%, and contains short-answer and extended-response questions. The IB's Physics curriculum update and official specimen papers show how these formats assess calculations, graphing, data interpretation and connected reasoning.
The recurring Fields (HL) question types
Although no topic is guaranteed to appear in one fixed form, Fields questions use a small number of highly reusable methods.
| Question pattern | Typical task | Main trap |
|---|---|---|
| Inverse-square field | Calculate or compare force and field strength | Using altitude instead of distance from the centre |
| Potential and energy | Find work, potential difference or escape speed | Losing the sign of gravitational or electric potential |
| Orbital motion | Derive speed, period or total energy | Treating gravitational force and centripetal force as separate forces |
| Field diagram | Draw field lines or equipotentials | Incorrect direction, spacing or intersections |
| Charged-particle motion | Determine force direction, radius or path | Ignoring the sign of the charge |
| Induction | Calculate flux or induced emf | Using the angle to the plane instead of the area normal |
| Explanation | Apply Lenz's law or explain energy transfer | Stating a direction without explaining opposition to change |
| Data-based problem | Interpret a graph, gradient or uncertainty | Calculating without referring back to the physical meaning |
Use the Topic D Fields hub to separate these patterns by subtopic rather than treating Fields as one large unit.
A reliable method for answering Fields questions
Identify the interaction before selecting an equation
Decide whether the question concerns a mass in a gravitational field, a charge in an electric field, a moving charge or current in a magnetic field, or a changing magnetic flux. Similar-looking diagrams can represent different physics.
Then identify the object experiencing the force. For example, electric field direction is defined using a positive test charge, but an electron accelerates opposite to that direction.
Draw directions and label distances
Add arrows for field, force, velocity and acceleration before calculating. For inverse-square equations, label the radial distance from the centre of the source object. If a satellite is at altitude h above a planet of radius R, the required distance is normally r = R + h.
For magnetic-force questions, mark whether the field is into or out of the page. Determine the force for a positive charge first, then reverse it if the particle is negative.
Write the governing relationship symbolically
Writing the equation before substitution makes method marks visible and helps expose incorrect models. For a circular orbit, begin with
gravitational force = centripetal force
GMm/r² = mv²/r
The satellite mass cancels, giving v = √(GM/r). Do not add a separate “centripetal force” to gravity. Centripetal force is the name for the resultant inward force, which gravity supplies in this case.
Finish with units, direction and interpretation
A numerical result is not always the complete answer. Include a direction for vector quantities and check whether the result is physically reasonable. A larger orbital radius should produce a lower orbital speed, while a stronger magnetic field should produce a smaller circular radius for the same particle momentum.
Core methods you must be able to apply
Gravitational and electric potential
Gravitational and electric fields share inverse-square mathematics, but their signs and physical behaviour differ.
| Quantity | Gravitational field | Electric field |
|---|---|---|
| Force | F = GMm/r², always attractive | F = k|Qq|/r², attractive or repulsive |
| Field strength | g = GM/r² | E = k|Q|/r² |
| Potential | Vg = -GM/r | Ve = kQ/r |
| Potential energy | Ep = mVg | Ep = qVe |
Potential is a scalar, so combine potentials algebraically before considering the force direction. Gravitational potential is negative when zero is defined at infinity because work must be supplied to remove a mass completely from an attractive gravitational field.
For potential-gradient questions, use the idea that the field points toward decreasing potential. In one radial dimension, this is represented by g = -ΔVg/Δr or E = -ΔVe/Δr. Closely spaced equipotentials therefore indicate a stronger field.
Orbital and escape calculations
For a circular orbit, gravity provides the centripetal force, leading to:
- orbital speed: v = √(GM/r)
- kinetic energy: Ek = GMm/(2r)
- gravitational potential energy: Ep = -GMm/r
- total orbital energy: Etotal = -GMm/(2r)
Escape speed follows from setting the final total energy at infinity equal to zero. Starting with ½mv² - GMm/r = 0 gives vesc = √(2GM/r). The escaping object's mass cancels, provided atmospheric resistance and additional propulsion are ignored.
Targeted practice in the D.1 gravitational fields questionbank helps distinguish orbit questions from escape questions.
Motion in electric and magnetic fields
In a uniform electric field, a charge experiences F = qE and therefore constant acceleration if relativistic effects are negligible. Between parallel plates, E = V/d when edge effects are ignored.
A magnetic field exerts F = qvB sin θ on a moving charge. When velocity is perpendicular to the field, the force remains perpendicular to the motion and produces a circular path:
qvB = mv²/r, so r = mv/(|q|B).
The magnetic force changes the direction of velocity but does no work, so the particle's speed and kinetic energy remain constant. Practise the distinction between electric acceleration and magnetic deflection using the D.2 electric and magnetic fields questions and D.3 electromagnetic motion questions.
Magnetic flux and induction
Magnetic flux is Φ = BA cos θ, where θ is the angle between the magnetic field and the normal to the coil's area. A coil with N turns has flux linkage NΦ. Faraday's law gives the magnitude of the average induced emf as N|ΔΦ/Δt|, while the negative sign in ε = -NΔΦ/Δt represents Lenz's law.
For direction questions, use this sequence:
- Identify whether the original magnetic flux is increasing or decreasing.
- State that the induced field opposes that change.
- Determine the required induced field direction.
- Use the appropriate hand rule to find the induced current.
Do not merely write “Lenz's law says it opposes the field.” The induced effect opposes the change in flux, not necessarily the original field itself. The D.4 induction questionbank provides focused practice with flux, generators and motional emf.
Why worked video solutions improve Fields performance
Re-reading notes can refresh definitions, but it does not reveal whether you can choose the correct model under exam conditions. A faster route to reliable method is to attempt a question without help, commit to a diagram and equation, and then watch the complete solution.
A useful practice cycle is:
- Attempt one Fields question under a short time limit.
- Mark the exact point where your reasoning changed direction or stopped.
- Watch the worked solution, pausing before each major step.
- Rewrite the solution from memory without copying.
- Attempt a parallel question one or two days later.
The value of a video is not passive viewing. It lets you observe equation selection, sign conventions, diagrams and mark-worthy explanations in sequence. RevisionDojo's IB Physics video solutions and lessons can be paired with the Physics Questionbank, while the IB Physics data booklet helps you practise locating equations at exam speed.
Common mistakes that lose marks
- Confusing field strength with force: g and E describe the field; F depends on the mass or charge placed in it.
- Ignoring signs: potential and potential energy may be negative even when their magnitudes are increasing.
- Using surface altitude as r: inverse-square formulas require distance from the source's centre.
- Treating potential as a vector: potentials add algebraically; fields and forces require direction.
- Forgetting charge sign: force direction reverses for a negative charge.
- Claiming magnetic force increases speed: a force perpendicular to velocity changes direction, not kinetic energy.
- Using the wrong flux angle: θ is measured from the area normal.
- Giving a law without applying it: an explanation must connect the principle to the stated situation.
- Hiding working: a calculator-only answer can lose method marks when the final value is wrong.
Conclusion
Success with IB Physics Fields (HL) questions depends on recognizing recurring structures rather than memorizing isolated answers. Draw the directions, identify the source and test object, select the physical model, work symbolically, and then check signs, units and physical meaning.
The quickest way to make this process automatic is to attempt questions before viewing their worked solutions. RevisionDojo's topic questionbanks, Jojo AI feedback and Physics video solutions can help you turn each mistake into a specific method to practise again.
Sources and referenced URLs
- Official IB Physics subject brief
- Official IB Physics curriculum update
- Official IB Physics specimen papers and markschemes
- RevisionDojo Topic D Fields hub
- RevisionDojo D.1 gravitational fields questionbank
- RevisionDojo D.2 electric and magnetic fields questionbank
- RevisionDojo D.3 motion in electromagnetic fields questionbank
- RevisionDojo D.4 induction questionbank
- RevisionDojo IB Physics video solutions and lessons
- RevisionDojo IB Physics Questionbank
- RevisionDojo IB Physics data booklet
