MAGNETISM Chapter 22

Magnetism  Magnetism is a force of attraction or repulsion due to an arrangement of electrons  The Magnetic forces usually are strongest at the two ends of the magnet. These are called poles 2

Poles  The end of the magnet that points toward the north is called the north magnetic pole. The other end that points south is the south magnetic pole.  The rule for magnetic poles is: Like poles repel, unlike poles attract 3

Magnetic Fields  The region in which magnetic forces can act is called a magnetic field 4

Magnetic Materials  Natural magnets – naturally occurring substances that have magnetic properties. ex: magnetite.  Magnetic induction – the process by which a material is made into a magnet. ex: stroking some materials in one direction with a strong magnet  Temporary magnets – materials that are easy to magnetize, but lose their magnetism quickly. ex: soft iron  Permanent magnets – materials that are more difficult to magnetize, but tend to stay magnetized. ex: cobalt, nickel and iron 5

Magnetic Materials cont.  Why are some materials magnetic while others aren’t?  Scientists believe that magnetism is due to the motion of electrons- particularly their spin.  All electrons spin and create a magnetic field around themselves. 6

Magnetic Materials cont.  Most electrons occur in pairs with opposite spins which cancel each others magnetic fields. Some metals contain electrons with unpaired electrons.  A region in which the magnetic fields of atoms are grouped together is called magnetic domain. The domains are randomly arranged in an un-magnetized object.  In a magnetized object the domains are aligned. 7

Electromagnetism  Electricity and magnetism are related. This is called electromagnetism  An electric current flowing through a wire gives rise to a magnetic field whose direction depends upon the direction of the current.  Coiling a conductor around a piece of soft iron will produce a powerful magnet. This is temporary and is only magnetic as long as current passes through the wire  The strength of an electromagnet can be increased two ways: ↑ the number of loops ↑ the voltage 8

Electromagnetic Induction  English scientist Michael Faraday discovered that electric current could be generated or induced by moving a wire through a magnetic field  The process by which a current is produced by the motion of a conductor (wire) in a magnetic field is called electromagnetic induction 9