Topic 12 and 13

• core

  The innermost part of something e.g. the central part of the Earth.
• induced magnet


  A piece of material that becomes a magnet because it is in the magnetic field of another magnet.
• magnetic field


  The area around a magnet where it can affect magnetic materials or induce a current.
• magnetic material


  A material, such as iron, that is attracted to a magnet.
• permanent magnet


  A magnet that is always magnetic, such as a bar magnet.
• plotting compass


  A small compass used to find the shape of a magnetic field.
• electromagnet

  A magnet made using a coil of wire with electricity flowing through it.
• solenoid


  A coil of wire with electricity flowing in it. Also called an electromagnet.
• temporary magnet


  A magnet that is not always magnetic, such as an electromagnet or an induced magnet.
• carbon brush


  A block of carbon that makes electrical contact between a circuit and a moving object such as a slip ring or commutator.
• Fleming's left-hand rule

  A way of remembering the direction of the force when a current flows in a magnetic field. The thumb shows the direction of the force, the first finger shows the direction of the magnetic field (N to S) and the second finger shows the current (+ to −).
• magnetic flux density


  A way of describing the strength of a magnetic field. It is measured in teslas (T).
• motor effect


  The force experienced by a wire carrying a current that is placed in a magnetic field.
• split-ring commutator


  A device attached to the rotating coil of a motor that makes electrical contact with an external circuit. A commutator switches over the connections every half-turn of the coil.
• tesla (T)


  The unit for magnetic flux density, also given as newtons per ampere metre (N/A m).
• alternating current (a.c.)


  Current which changes direction many times each second.
• alternator


  A generator that produces alternating current.
• carbon brush


  A block of carbon that makes electrical contact between a circuit and a moving object such as a slip ring or commutator.
• commutator


  A device attached to the rotating coil of a generator that makes electrical contact with an external circuit. A commutator switches over the connections every half-turn of the coil so the output is a form of direct current.
• diaphragm


  A thin sheet of flexible material.
• direct current (d.c)


  Current that always flows in the same direction.
• dynamo

  A generator that uses a commutator to change its output from alternating current to direct current.
• generator


  A machine that produces electricity by rotating coils of wire in a magnetic field (or by rotating magnets near a coil of wire).
• induce


  To create. For example, a wire in a changing magnetic field has a current induced in it.
• loudspeaker


  A machine for converting changes in electrical current or voltage into sound waves.
• microphone


  A machine for converting sound waves into changes in electrical current or voltage.
• potential difference (p.d.)


  The difference in the energy carried by electrons before and after they have flowed through a component. Another term for voltage.
• slip ring


  Metal rings connected to the rotation coil in a generator. They make electrical contact with an external circuit.
• voltage


  The difference in the energy carried by electrons before and after they have flowed through a component. Another term for potential difference.
• national grid

  The system of wires and transformers that distributes electricity around the country.
• primary coil


  The coil in a transformer to which the electricity supply is connected.
• secondary coil

  The coil in a transformer where the changed voltage is obtained.
• step-down transformer

  A transformer that reduces the voltage.
• step-up transformer

  A transformer that increases the voltage.
• transformer


  A device that can change the voltage of an electricity supply.
• transmission lines

  The wires (overhead or underground) that take electricity from power stations to towns and cities.
• coulomb (C)


  The unit of electric charge. One coulomb is the charge that passes a point in a circuit when there is a current of 1 ampere for 1 second.
• power

  The amount of energy (in joules, J) transferred every second. It is measured in watts (W).