Curriculum Portal

neurologyYou need to know

• A magnetic field is the region around a magnet, magnetic material, or current-carrying conductor where a magnetic force can act.
• Magnetic field lines show the shape and direction of a magnetic field, and they point from the north pole to the south pole outside a magnet.
• A stronger magnetic field is shown by magnetic field lines that are closer together.
• Like magnetic poles repel each other, and unlike magnetic poles attract each other.
• A magnetic compass needle lines up with the Earth's magnetic field, so its north-seeking end points towards the Earth's magnetic north pole region.
• Iron, steel, nickel and cobalt are magnetic materials that can become induced magnets when placed in a magnetic field.
• Induced magnetism happens when a magnetic material becomes magnetised in a magnetic field; induced magnets are usually attracted to the magnet inducing them.
• The magnetic force between two magnets gets weaker as the distance between the magnets increases.
• A current flowing through a conductor produces a magnetic field around the conductor.
• The magnetic field around a straight current-carrying wire forms concentric circles centred on the wire, and reversing the current reverses the field direction.
• A solenoid is a coil of wire, and its magnetic field is similar in shape to the field of a bar magnet, with a north pole at one end and a south pole at the other.
• The magnetic field inside a solenoid is strong and uniform because the fields from each turn of wire add together in the same direction.
• The strength of an electromagnet increases when the current increases, the number of turns of wire increases, or an iron core is added.
• A current-carrying conductor in an external magnetic field experiences a force when the conductor is not parallel to the magnetic field.
• The size of the force on a current-carrying conductor in a magnetic field is given by `F = BIL` when the conductor is at right angles to the field, where `F` is force, `B` is magnetic flux density, `I` is current and `L` is length in the field.
• The motor effect is the force on a current-carrying conductor in a magnetic field, and it is used in electric motors and loudspeakers.
• The generator effect happens when a conductor cuts through magnetic field lines, or experiences a changing magnetic field, causing an induced potential difference and sometimes an induced current.
• Lenz's law states that the magnetic field produced by an induced current opposes the change that caused the current.
• A dynamo generates direct current, whereas an alternator generates alternating current.
• A transformer has a primary coil, a secondary coil and an iron core, and for an ideal transformer the voltage ratio is given by `V_p/V_s = N_p/N_s`.

• Plot a magnetic field pattern using a compass by marking the needle direction at several points and joining the marks with field lines from north to south.
• Draw magnetic field patterns around a bar magnet, between attracting poles and between repelling poles, showing direction with arrows and strength by line spacing.
• Investigate how magnetic force varies with distance by changing the separation between magnets, measuring the force with a newton meter or balance, and controlling other variables.
• Draw the magnetic field around a straight current-carrying wire and around a solenoid, using the correct field shape and direction for the current shown.
• Investigate electromagnet strength by varying current, number of coil turns, or core material one at a time, and measuring strength using the mass lifted or number of paper clips held.
• Use Fleming's left-hand rule to predict force direction, with the first finger for field, second finger for current and thumb for force.
• Calculate the force on a current-carrying conductor using `F = BIL`, selecting the correct values and units for magnetic flux density, current and length in the field.
• Explain the operation of a motor, loudspeaker, generator, microphone or relay by linking current, magnetic fields, forces, motion and energy transfers in the correct sequence.
• Draw and interpret graphs of induced potential difference against time for dynamos and alternators, identifying direct current and alternating current outputs.
• Calculate transformer input or output voltage using `V_p/V_s = N_p/N_s`, and identify whether the transformer is step-up or step-down from the coil turns and voltages.