P4: Magnetism and magnetic fields

P4.1 Magnets and magnetic fields

P4.1a describe the attraction and repulsion between unlike and like poles for permanent magnets

P4.1b describe the difference between permanent and induced magnets

P4.1c describe the characteristics of the magnetic field of a magnet, showing how strength and direction change from one point to another

P4.1d explain how the behaviour of a magnetic (dipping) compass is related to evidence that the core of the Earth must be magnetic

P4.1e describe how to show that a current can create a magnetic effect and describe the directions of the magnetic field around a conducting wire

P4.1f recall that the strength of the field depends on the current and the distance from the conductor

P4.1g explain how solenoid arrangements can enhance the magnetic effect

P4.2 Uses of magnetism

PM4.2i apply: force on a conductor (at right angles to a magnetic field) carrying a current (N) = magnetic flux density (T) x current (A) x length (m)

PM4.2ii apply: potential difference across primary coil (V)/ potential difference across secondary coil (V) = number of turns in primary coil / number of turns in secondary coil

P4.2a describe how a magnet and a current-carrying conductor exert a force on one another

P4.2b show that Fleming’s left-hand rule represents the relative orientations of the force, the conductor and the magnetic field

P4.2c apply the equation that links the force on a conductor to the magnetic flux density, the current and the length of conductor to calculate the forces involved

P4.2d explain how the force exerted from a magnet and a current-carrying conductor is used to cause rotation in electric motors

P4.2e recall that a change in the magnetic field around a conductor can give rise to an induced potential difference across its ends, which could drive a current, generating a magnetic field that would oppose the original change

P4.2f explain how this effect is used in an alternator to generate a.c., and in a dynamo to generate d.c

P4.2g explain how the effect of an alternating current in one circuit, in inducing a current in another, is used in transformers

P4.2h explain how the ratio of the potential differences across the two depends on the ratio of the numbers of turns in each

P4.2i apply the equations linking the potential differences and numbers of turns in the two coils of a transformer, to the currents (M1c, M3b, M3c)