Transcript 0329magnets.ppt.pptx

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