Concept of a magnetic field
Cambridge A-Level Physics (9702) · Unit 20: Magnetic fields · 6 flashcards
Concept of a magnetic field is topic 20.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 20 — Magnetic fields , alongside Force on a current-carrying conductor, Force on a moving charge and Magnetic fields due to currents. In one line: A magnetic field is a region of space where a moving charge or magnetic material experiences a force. It is a vector field, possessing both magnitude and direction.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 6 flashcards — 3 definitions and 3 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
A magnetic field
A magnetic field is a region of space where a moving charge or magnetic material experiences a force. It is a vector field, possessing both magnitude and direction.
What the Cambridge 9702 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- understand that a magnetic field is an example of a field of force produced either by moving charges or by permanent magnets
- represent a magnetic field by field lines
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Concept of a magnetic field
- › Magnetic field strength B decreases with distance; ensure concentric circles representing the field lines get further apart as distance from the wire increases.
- › Attribute Hall voltage to the deflection of charge carriers by a magnetic field, not to the principles of induction.
- › Always include the 'at right angles' or 'perpendicular' condition when defining B = F / (Il).
- › Always follow the logical sequence: changing flux linkage induces an e.m.f., which then causes a current if the circuit is complete.
- › Always specify that the magnetic force acts on a moving charged particle or a current-carrying conductor.
Define a magnetic field.
A magnetic field is a region of space where a moving charge or magnetic material experiences a force. It is a vector field, possessing both magnitude and direction.
What are the two sources that produce magnetic fields?
Magnetic fields are produced either by moving electric charges (electric current) or by permanent magnets due to the intrinsic magnetic dipole moment of elementary particles such as electrons.
Describe how magnetic field lines are used to represent a magnetic field.
Magnetic field lines indicate the direction of the force that a north magnetic pole would experience. The density of the lines indicates the strength of the field; closer lines mean a stronger field.
What determines the direction of a magnetic field line?
The direction of a magnetic field line at any point is the direction of the force on a 'north' magnetic pole at that point. The field lines always point from the north pole to the south pole outside the magnet.
How does the strength of the magnetic field relate to the spacing of magnetic field lines?
The closer the magnetic field lines are to each other, the stronger the magnetic field is in that region. Conversely, widely spaced lines indicate a weaker field.
Why is a magnetic field considered a 'field of force'?
A magnetic field is a region where a force is exerted on specific objects. In this case, the specific objects are moving electric charges and magnetic dipoles.
Review the material
Read full revision notes on Concept of a magnetic field — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 20 — Magnetic fields
Concept of a magnetic field sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Concept of a magnetic field deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Concept of a magnetic field deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Rate each card Hard, Okay, or Easy after flipping.