Unit 4 Day 10 – Magnetic Materials & Electromagnets Ferromagnetic Materials Ferromagnetism at the Atomic Level Electromagnets & Their Applications

Ferromagnetic Materials Magnets made with iron are said to be ferromagnetic materials Inside iron are small “domains” which are 1 mm regions whose ions are polarized to form dipoles These domains are randomly oriented in an “unmagnetized” piece of iron so that the magnetic effects cancel each other out

Ferromagnetic Materials In a magnetized piece of iron, the domains are generally aligned in one direction Iron can become magnetized by placing it in a strong magnetic field Heating or mechanically hammering a magnet will cause it to lose its magnetization If iron is heated above the “Curie Temperature” (1043 K for iron) a magnet can not be made magnetic at all.

Ferromagnetism at the Atomic Level Electrons in orbit about a nucleus are charged & therefore constitute an electric current The rotating electrons produce a magnetic field but the motions are in random directions, therefore the magnetic fields add up to zero Electric current is also thought to be produced by electron spin. This is what Physicists believes causes ferromagnetism Today, it is believed that all magnetic fields are caused by electric currents. This means that magnetic fields always form closed loops!

Electromagnetic & Their Applications A piece of hard iron (permanent magnet) placed in a current producing coil forms an “electromagnet”. In an electromagnet, the iron material’s magnetic field adds to the solenoid’s field, resulting an a magnetic field x100 stronger Use for solenoid electromagnets are: doorbells, morors, switches (relays), magnetic circuit breakers

Solenoid Electromagnets Door Bell Relay Circuit Breaker