Electricity & Magnetism is a core part of IB Physics. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Current & voltageFlow of charge and the energy per unit charge driving it.
ResistanceOpposition to current flow; V = IR.
Magnetic fieldRegion where a magnetic material or current feels a force.
ElectromagnetA current-carrying coil that acts as a magnet.
Motor effectA current-carrying wire in a magnetic field experiences a force.
Electromagnetic inductionA changing magnetic field induces a potential difference.
Faraday's lawInduced EMF = -d(flux)/dt; magnitude proportional to rate of change of magnetic flux (Faraday 1831).
Lenz's lawDirection of induced current opposes the change producing it; conserves energy (Lenz 1834).
TransformerVp/Vs = Np/Ns for ideal transformer; AC induces flux change in iron core.
Eddy currentsInduced loops in solid conductors dissipate energy; laminated cores reduce them.
RMS current/voltageI_rms = I_peak / sqrt 2 for sinusoidal AC; equivalent DC for same power dissipation.
AC generatorCoil rotates in magnetic field producing sinusoidal EMF; brushes and slip rings carry current.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Which way do magnetic field lines point outside a magnet?✗ From south to north. ✓ From the north pole to the south pole.
Are all metals magnetic?✗ Yes, all metals are attracted to magnets. ✓ No — only iron, steel, nickel and cobalt.
What does the motor effect need?✗ A still wire with no current near a magnet. ✓ A current in a wire placed within a magnetic field.
Practise Electricity & Magnetism — free games
Test yourself with these quick revision games for this topic:
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