Inside a Magnet Chapter 1, Section 2, p14-19

The Atom Magnetic properties of materials depend on structure of its atoms Matter: anything that has mass and takes up space All matter is made of atoms Atom: smallest particle of an element Element: one of about 100 basic substances that make up all matter Structure and composition of atoms that make up an element makes that element different from other elements

Structure of an Atom Nucleus: center region of an atom Two kinds of particles are found inside nucleus: Proton: particle that carries a positive charge Neutron: particle that doesn’t carry any charge The outer region is mostly empty space Electron: particle that carries a negative charge Move randomly through atom Much smaller than neutrons & protons

Electron Spin Each electron behaves like it is spinning, so it has a property called “electron spin” A spinning electron produces a magnetic field that makes the electron behave like a tiny magnet in an atom Most atoms have paired electrons spinning in opposite directions Opposite spin = opposite magnetic fields = cancel out Most atoms have weak magnetic properties Some atoms have unpaired electrons = strong magnetic properties

Magnetic Domains Magnetic fields of atoms in most materials point in random directions Magnetic fields cancel one another Weak magnetic force that you can’t detect Magnetic fields of many atoms are aligned with each other in some materials Magnetic domain: group of atoms that have their magnetic fields aligned Domain acts like a bar magnet with north & south poles

Alignment of Domains Direction domains point determines if the material is magnetized or not Magnetic domains point in random directions Cancel each other out = not magnetized Magnetic domains pointing in the same direction In magnetized material, all or most of the magnetic domains are arranged in same direction Magnetic fields of domains are aligned

Magnetic Materials Materials can be a strong magnet if it’s magnetic domains align Ferromagnetic material: material that shows strong magnetic properties Ferrum means “iron” (Fe) Ferromagnetic material placed in a magnetic field acts like iron Common ferromagnetic materials: Iron, Nickel, Cobalt, Gadolinium Rare elements: Samarium & Neodymium

Magnetic Materials Some magnets made from several different materials Alloy: combination of several metals Alnico: Al uminum N ickel I ron Co balt Powerful magnets: Platinum & Cobalt Cobalt & Neodymium

Magnetic Materials Ferrite – most commonly used material to make magnets today Mixture of substances containing ferromagnetic elements Brittle material that chips easily Usually stronger & less expensive than metal magnets of same size

Making & Changing Magnets Magnets can be made, destroyed or broken apart Magnets can be made from ferromagnetic materials No magnet can last forever

Making Magnets Magnets can be made by: Placing unmagnetized ferromagnetic material in a strong magnetic field Rubbing a ferromagnetic material with one pole of a magnet Rub in one direction Causes magnetic domains to line up in same direction More domains lined up = more magnetic Steel in paper clip / pure iron easy to magnetize

Making Magnets Temporary magnet: magnet made from a material that easily loses its magnetism Permanent magnet: magnet made from a material that keeps its magnetism for a long time

Destroying Magnets Permanent magnets can also become unmagnetized just like temporary magnets Drop it / strike it hard Magnetic domains knocked out of alignment Heat it Particles vibrate faster and more randomly Difficult for domains to stay lined up with movement Every ferromagnetic material loses its magnetism a certain temperature Temperature depends on material

Breaking Magnets What happens if you break a magnet in half? You have two smaller magnets Each smaller magnet has its own north & south poles Figure 11 Magnet has many magnetic domains lined up in one direction Many north and south poles are all facing each other Produces strong magnetic force at poles (N) & (S) The domains in two halves still line up when cut in half Many north or south poles will still be at each end

Homework Read Chapter 1, Section 2, p14-19 Answer ?s 1-3 p19