A region where a magnetic force is being exerted is known as a magnetic field.- Opposite poles attract, like poles repel.
- Magnetic field lines run from north to south.
A region where a magnetic force is being exerted is known as a magnetic field.- The catapult effect is due to the magnetic force cancelling out forces which are moving in the opposite direction to the magnetic field lines.
- If a current passing through a wire in a magnetic field exerts a force on the wire this is called the motor effect.
- The force can increased by using stronger magnet or increasing the current.
- The size of the force depends on the angle at which the magnetic field lines and the wire.
An electric motor uses the motor effect and its speed can be altered by changing the current.- The armature coil of an electric motor is forced to rotate when a current passes through it.
- Each half-turn the direction in which the coil is traveling is reversed by the split ring commutator.
- A generator is composed of coils of wire that rotate within a magnetic field.
- In a complete circuit the creation of a potential difference leads to an electric current which is able to travel through the circuit.
- If an piece of insulated wire is connected to an ammeter then moved between the poles of a U-shaped magnet a current is produced each time the magnetic field line is cut by the wire. This is called the dynamo effect.
- Forcing a rectangular coil to rotate within a magnetic field it’s possible to make a simple alternating current (AC) generator.
A National Grid transformer is made from an iron core around which is wound two insulated wire coils: the primary coil and the secondary coil.- As an alternating current travels through the primary coil this induces an alternating potential difference in the secondary coil which produces a current.
- A transformer only uses an alternating current because an alternating secondary potential difference can’t be created by a direct current.
- The potential difference is increased when transferred from the power station to the National Grid by step-up transformers.
- The potential difference is decreased when transferred from the National Grid to the mains by step-down transformers.
- The secondary potential difference is dependant on the primary potential difference as well as the number of turns on both of the coils.
- VP/VS = NP/NS
- In a step-up transformer: VS is more then VP and NS is more than NP.
- In a step-down transformer: VS is less then VP and NS is less than NP.
- If a transformer is 100% efficient: IPVP = ISVS
An electric motor uses the motor effect and its speed can be altered by changing the current.