Section 16:1 Magnets and Magnetism Notes

Properties of Magnets Any material that attracts iron or things made of iron is called a magnet. Any material that attracts iron or things made of iron is called a magnet. Have two poles Have two poles Exert magnetic forces Exert magnetic forces Are surrounded by a magnetic field Are surrounded by a magnetic field

Magnetic poles Magnetic poles are points on a magnet that have opposite magnetic qualities. Magnetic poles are points on a magnet that have opposite magnetic qualities. The pole of the magnet that points to the north is called the magnet’s north pole. The pole of the magnet that points to the north is called the magnet’s north pole. The pole of the magnet that points to the south is called the magnet’s south pole. The pole of the magnet that points to the south is called the magnet’s south pole. Magnetic poles are always in pairs. Magnetic poles are always in pairs.

Magnetic Forces Magnetic force- the force of attraction or repulsion generated by moving or spinning electric charges Magnetic force- the force of attraction or repulsion generated by moving or spinning electric charges Like poles repel. Like poles repel. Opposite poles attract. Opposite poles attract. The magnetic force of a magnet is strongest at the poles. The magnetic force of a magnet is strongest at the poles.

Magnetic Fields The area surrounding a magnet in which the magnetic force exists is called the magnetic field. The area surrounding a magnet in which the magnetic force exists is called the magnetic field. The shape of the field can be shown with magnetic field lines. The shape of the field can be shown with magnetic field lines. The closer together the field lines are, the stronger the magnetic field is. The closer together the field lines are, the stronger the magnetic field is.

Atoms and Domains As an electron moves around an atom, it makes, or induces, a magnetic field. As an electron moves around an atom, it makes, or induces, a magnetic field. If the magnetic fields of the individual atoms cancel each other out, the material is not magnetic. If the magnetic fields of the individual atoms cancel each other out, the material is not magnetic. Groups of atoms are in tiny areas called domains. Groups of atoms are in tiny areas called domains. A material is magnetic if its domains line up. A material is magnetic if its domains line up.

Losing Alignment When domains move, the magnet is demagnetized, or loses its magnetic properties. When domains move, the magnet is demagnetized, or loses its magnetic properties. A magnet can lose its magnetic properties if it is dropped, hit, placed in a strong magnetic field that is opposite of its own, or heated. A magnet can lose its magnetic properties if it is dropped, hit, placed in a strong magnetic field that is opposite of its own, or heated.

Making Magnets You can make a magnet from something made of iron, cobalt, or nickel. You can make a magnet from something made of iron, cobalt, or nickel. You just need to line up the domains in it. You just need to line up the domains in it.

Cutting a Magnet When you cut a magnet in half, you end up with two magnets. When you cut a magnet in half, you end up with two magnets. Each piece has its own north pole and south pole. Each piece has its own north pole and south pole.

Kinds of Magnets Magnets made of iron, nickel, cobalt, or mixtures of these metals have strong magnetic properties and are called ferromagnets. Magnets made of iron, nickel, cobalt, or mixtures of these metals have strong magnetic properties and are called ferromagnets. An electromagnet is a magnet made by an electric current. An electromagnet is a magnet made by an electric current. An electromagnet usually has an iron core. An electromagnet usually has an iron core.

Temporary and Permanent Magnets Temporary magnets are made from materials that are easy to magnetize. Temporary magnets are made from materials that are easy to magnetize. But they tend to lose their magnetization easily. But they tend to lose their magnetization easily. Example: soft iron Example: soft iron Permanent magnets are difficult to magnetize. Permanent magnets are difficult to magnetize. But they tend to keep their magnetic properties longer than temporary magnets do. But they tend to keep their magnetic properties longer than temporary magnets do. Example: alnico Example: alnico

Earth as a Magnet Earth acts as if it has a big bar magnet through its core. Earth acts as if it has a big bar magnet through its core. Compass needles and the north poles of magnets point to Earth’s magnetic south pole, which is near Earth’s geographic North Pole. Compass needles and the north poles of magnets point to Earth’s magnetic south pole, which is near Earth’s geographic North Pole. The Earth’s magnetic field is caused by the movement of electric charges in Earth’s liquid outer core. The Earth’s magnetic field is caused by the movement of electric charges in Earth’s liquid outer core. Auroras are most commonly seen near Earth’s magnetic poles because Earth’s magnetic field bends inward at the poles. Auroras are most commonly seen near Earth’s magnetic poles because Earth’s magnetic field bends inward at the poles.