Uses of electromagnetism
Lifting scrap ferromagnetic metals
Electromagnets can be usefully employed to move scrap metal from one place to another.
When the current is switched off the magnet losses its magnetism and the car falls back to the ground.
The image below shows a typical cross-section through an industrial electromagnetic lifting device:
Electromagnets can be turned off. When used for lifting scrap metal from one place to another, the crane operator can lower a large disc onto a pile of scrap metal and then switch on the electromagnet. The large disc and the scrap are then lifted. The scrap can be dropped anywhere by simply switching off the electrical supply to the electromagnet.
Electromagnetic electric bells have been used for many years.
When the switch is on, current proceeds to flow through the electromagnet. A magnetic field is generated around the coil which, in turn, attracts the soft iron. Attached to the soft iron is a hammer which strikes the bell. As soon as the bell is struck the electrical circuit is broken and the soft iron returns to rest on the threaded contact. The current proceeds to flow through the electromagnet again and the process keeps repeating until the circuit is switched off.
Electromagnets are used extensively in loudspeakers.
The frequency of the vibrations of sound can be transported electrically as changes in electrical flow.
A loudspeaker can take these changing electrical flows through an electromagnet attached to a cone. Changes in the current flow alter the strength of attraction to the permanent magnet, moving the electromagnetic coil in and out. Soft, quiet sounds move slowly; loud, harsh sounds move violently and strongly. This results in a vibration of the speaker cone which creates the sound waves that are received by our ears.