Magnets

• ​Magnets have two ends called poles

  • North and South pole

  • There are no single pole magnets

• Like poles repel, opposite poles attract ​

• It was discovered that running a current through a wire produced a magnet

• The magnetism around permanent magnets and currents are very similar, so both must have a common cause.

• Current is the cause of all magnetism ​

Electromagnetism

Ferromagnetism

• Magnetic materials have an unpaired outer electron.

• Atoms near each other line up so that the unpair electrons spin in the same direction.

• This spinning of electrons creates magnetism.​

Ferromagnetism

• ​In permanent magnet the current is electrons in atoms.​

  • Move around nucleus and spin​

  • Most cancels out except in ferromagnetic materials​

• Ferromagnetic materials

  • Electron magnetic effects don’t cancel over large groups of atoms.

  • This gives small magnetic regions size of 0.01 to 0.1 mm called magnetic domains.

  • In a permanent magnet, these domains are aligned.

• Common magnetic materials are iron, nickel, cobalt, and chromium dioxide.​

Induced Magnetism

• Usually magnetic domains are randomly arranged

• When it is placed in a B-field (magnetic field), the domains that are aligned with the B-field grow larger and the orientation ​of other domains may rotate until they are aligned.

• This gives the material overall magnetism.

• Dropping or banging a permanent magnet can disalign the magnetic domains and thus have a weaker B-field.

• The induced B-field can be 1000’s of time larger than the field that induced it, so electromagnets have iron cores wrapped with wire.