Transcript Magnetism
Magnetism E. Q. – What is magnetism and how does it affect our everyday lives? What is a magnet? • The definition of a magnet is anything that is surrounded by a magnetic field and attracts iron or steel particles to it. • A magnetic field is the area around a magnet where magnetic force can be felt. • All magnets have two poles, named the North Pole and the South Pole. • All metals are not attracted to magnets—only iron and steel are attracted. • Magnets can occur naturally or they can be man-made. • Magnets can be permanent or just temporary. Some magnets can be turned on and off. • The ancient Greeks discovered natural magnets in the area called Magnesia, and that’s how magnets got their name. What causes magnetism? • Just as electricity is caused by • This still doesn’t make a magnet the movement of electrons, so is because the atoms’ poles are all magnetism. pointing in different directions. • Electrons moved from place to • If the atoms can be shifted so that place causes electricity. their poles point in the same • Magnetism is caused by the direction, then a magnet is created. spinning of electrons as they Non-magnet Magnet move. • In the atoms of almost all elements, about half of the electrons spin clockwise and half spin counterclockwise. • In the atoms of magnets, most of the electrons spin in one direction and makes the atoms have “poles.” What’s the biggest magnet? • The Earth itself is a • huge magnet. • The Earth’s magnetic properties guide such • migrating animals as birds, whales, and butterflies on yearly journeys. • Compass needles are attracted to the Earth’s magnetic North Pole and helped explorers sail safely out of sight of land. The Earth’s magnetic poles and geographic poles are not exactly in the same place. Compass needles point to the magnetic North Pole, not the geographic North Pole. Geographic North Pole Magnetic North Pole Equator What kinds of magnets are there? • There are natural magnets and man-made magnets. • There are temporary magnets and permanent magnets. The electromagnet in this picture is manmade and also temporary. It only works when electric current flows through the coil. The rock in the picture is magnetite, which is a natural magnet. It is also permanent. Magnetic Fields • The magnetic field around a magnet is always strongest at the poles of the magnet. • You can see the lines of force if you sprinkle iron filings on a piece of paper on top of a magnet. What affects a magnet’s strength? A permanent magnet can be weakened by -- hitting it dropping it heating it An electromagnet can be strengthened by -- adding more nails to the iron core of the magnet wrapping more turns of wire into the coil increase the voltage of the electric source. What happens when you break a magnet? • A magnet always has two poles; North and South. • If you break a magnet in half, you get TWO magnets, each having two poles; North and South. • No matter how small the magnets get there will always be two poles; North and South! The Rule of Magnetic Poles • This is also called Coulomb’s Law. • It says that opposite poles attract and like poles repel. Can Electricity cause Magnetism? • When electricity flows through a coil of wire, it causes a magnetic field around the wire. • Put the wire coil between two permanent magnets. • If the current changes direction, the poles of the magnet are reversed. • The commutator changes the direction of current in the wire so that the coil keeps moving in a circle. • The rotating coil spins, changing electric energy to mechanical energy. • This is an electric motor. Can Magnetism cause Electricity? • Moving a magnet through the middle of a coil of wire or moving the coil through a magnetic field makes electricity to flow through the wire. • This is an electric generator, which changes mechanical energy to electrical energy. Uses of Magnetism? • • • • • • • • • • Magnetism makes lots of modern conveniences possible: Electric generators Electric motors Stereo speakers Telephones Tape recorders Junkyard electromagnets Latches on refrigerator doors Transformers Many many more!