Magnets

Students will learn about magnets (Chapter 24 and Review pp. 133-36.)

Lodestones

• Chinese and Greeks knew that naturally occurring lodestones attracted iron

• When pieces of iron were rubbed with lodestones, they became magnetized.

• If a very thin piece of magnetized iron was floated on water, one end always pointed north.

• Chinese thus created compasses.

Earth is a magnet

• Because of iron and nickel in its core, the earth is a magnet.

• Geographic north pole is magnetic south• Geographic south pole is magnetic north• The earth has switched polarity (Examine

magnetic rocks on the sea floor).

Elements that are magnetic

• Iron, Nickel, and cobalt are common magnetic elements

• ALNICO is an alloy of iron, aluminum, nickel and cobalt

Subatomic Causes for magnets

• Unpaired electrons spin.• When many many unpaired electrons align

their spins so they spin in the same direction, they create magnets.

Isolate the north pole?

• If you try to isolate the north pole by itself by cutting a bar magnet, new poles would form on the ends of the magnet.

Magnetic field lines

• Magnetic field lines go from North to South.• Within a magnet these lines are closed loops.

Electromagnetism

• In 1820 Hans Oersted discovered that a wire carrying current created a magnetic field.

• If the direction of the conventional current is upward, use the right hand rule to show the direction of the magnetic field. The thumb points in the direction of conventional current and the fingers point in the direction of the magnetic field. (N.B. perpendicular).

Polarity

• Magnets have polarity.• The end that points northward is the north

pole.• The end that points southward is the south

pole.• Like poles repel each other• Unlike poles attract reach other