Magnetic fields

About this lab: Magnetic fields

Interactive simulation for Cambridge A Level Physics 9702 topic 20 Magnetic fields: field lines of a bar magnet and of two magnets facing with plotting compasses, the fields of a straight wire (B = μ₀I/2πd), a flat coil and a solenoid with the grip rule and the force between parallel wires, the force on a current F = BIL sin θ with Fleming's left-hand rule and a current balance, a charge circling in a field with r = mv/BQ, a velocity selector and the Hall effect, and Faraday's and Lenz's laws with a magnet pushed through a coil and a rotating generator coil.

Field patterns and plotting compasses, the fields of wires, coils and solenoids, the force on a current and on a moving charge, the Hall effect, and electromagnetic induction

Magnetic fields is a free, browser-based simulation for Cambridge International AS & A Level Physics 9702 (topic 20 Magnetic fields). The course is assessed in Paper 1 (multiple choice), Paper 2 (AS structured), Paper 3 (advanced practical), Paper 4 (A Level structured) and Paper 5 (planning, analysis and evaluation). There are 5 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.

Syllabus coverage

• 20.1 Concept of a magnetic field: B-fields from moving charges and permanent magnets; Field-line representation. Lessons: Magnetic fields and field lines.
• 20.2 Force on a current-carrying conductor: F = BIL sin θ and Fleming's left-hand rule; Magnetic flux density: definition from F = BIL. Lessons: Force on a current-carrying conductor.
• 20.3 Force on a moving charge: F = BQv sin θ and direction of force; The Hall voltage: V_H = BI ÷ (ntq); Hall probe to measure flux density; Circular motion of charges in perpendicular B-fields; Velocity selectors: crossed E and B fields. Lessons: Force on a moving charge.
• 20.4 Magnetic fields due to currents: B-field patterns: wire, coil, solenoid; Ferrous core effect in solenoids; Forces between current-carrying conductors. Lessons: Magnetic fields due to currents.
• 20.5 Electromagnetic induction: Magnetic flux: Φ = BA; Magnetic flux linkage; Demonstrating induced e.m.f.s; Faraday's and Lenz's laws. Lessons: Electromagnetic induction.

Full syllabus map: A Level Physics 9702 topic 20.

How to use this simulation

1. 1. Fields and field lines.
2. 2. Fields due to currents.
3. 3. Force on a conductor.
4. 4. Force on a moving charge.
5. 5. Electromagnetic induction.
6. The buttons at the end of the tab strip give the scene the whole window (Full screen, Hide controls) and, on a dark stage, a projector-friendly palette (Light scene). Many scenes also have drag handles: drag them to change the set-up directly.

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