Lemon Shark (Negaprion brevirostris)

Magnets are familiar strangers. Most of us have at least one around the house - in our telephone receivers, stereo and TV speakers, or used to turn our refrigerators into bulletin boards and art galleries. The earliest magnets (circa 500 BC) were naturally-occurring lumps of an iron oxide mineral known as 'magnetite' (Fe3O4) and were imputed with all manner of mystical properties. Today, magnets come in all shapes and sizes: from simple bars and 'classic' horseshoes to various business logos and cartoon characters to food, fishes, cows, and even baby-blue pigs with 'Think Thin' written across their bellies - thereby holding up both our best intentions and our kids' baseball schedules. Magnets are everywhere. But few of us understand how they work.

Magnetism and electricity are fundamentally interconnected. Danish scientist Hans Christian Oersted showed in 1820 that an electric current flowing in a wire deflects a compass nearby. Whenever an electric current flows - whether from cloud to ground in the form of lightning or through a contracting muscle in the body - a magnetic field is created. The unification of electric and magnetic principles under a comprehensive mathematical theory was first achieved by Scottish physicist James Clerk Maxwell in 1864. It is now known that magnetism is a property of the atom itself. Ultimately, the magnetic properties of matter are determined by the collective behavior of the negatively charged electrons that orbit the nuclei of atoms. The magnetic dipole moment (or magnetic field) of an individual electron has two components, one resulting from the spin of the electron about its own axis, the other from its orbital motion about the nucleus. Both kinds of motion may be considered as tiny circular currents (moving charges), thus linking electricity and magnetism at an atomic level.

In most atoms and molecules, these electronic magnets are oriented in random directions and the sum total magnetic moment of all the orbital electrons is zero. However, in some highly ordered crystalline materials - such as iron, nickel, and cobalt - the spins of some orbital electrons in adjacent atoms become coupled (I will spare you the quantum physics), creating local magnetic 'domains' in which magnetization is unidirectional. Adjacent domains are magnetized in different directions, so that there is no bulk magnetization. When an external magnetic field is applied, those domains aligned with the field grow at the expense of others, resulting in a very strong type of permanent magnetization known as 'ferromagnetism'. So from where does this 'external field' come? For the answer, we must look to the Earth's core....Read on...http://www.elasmo-research.org/education/topics/s_lodestones.htm

Posted by Jay Roberts at 10:03 PM | Permalink