Physics GCSE: Magnetism and Electromagnetism
Uses of electromagnetism
A huge electromagnet is often used to pick up cars. When the current is switched off, the magnet loses its magnetism and the car falls back down to the ground.
An electric motor uses the motor effect to spin a coil of wire inside a magnetic field.
To increase the speed of the motor: - Increase the current in the coil.
- Increase the number of loops on the spinning coil.
- Increase the strength of the magnet.
If either the magnetic poles are swapped around or the current flows in the opposite direction the motor will spin in the opposite direction.
The alternating current that represents a sound wave flows through the coil. As the current carrying coil is inside a magnetic field a force is produced, which makes the coil move. This pulls the paper cone in the same direction. As the current changes direction, the force produced changes direction. This makes the paper cone move the opposite way. The backward and forward motion of the cone produces a sound wave in the air.
The higher the frequency of the electrical signal, the higher the frequency of the sound wave produced, so making a higher pitched noise. The greater the amplitude of the electrical signal, the greater the force produced, so the further the cone will move, making a louder noise.
Relays are used as safety devices. A large current circuit can be switched on by a small current circuit, as shown below:
When the small current in the input circuit is switched on, the electromagnet becomes magnetic and attracts the iron armature. The armature rotates towards the electromagnet, pushing the contacts together. This switches on the large current in the output circuit.
This type of relay circuit is used in the ignition of a car.
