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Magnetism
• A magnet is an object that can attract other objects
containing iron, cobalt, or nickel.
• Magnetic substances are created when electrons from
within the atom or from another atom spins in the same
direction – this increases the magnetic field given off by
the electron (each spinning electron creates its own tiny
magnetic field)
• The spinning of electrons in the same direction causes a
north and south pole to form.
• Every magnet has at least one north pole and one south
pole.
• If you take a bar magnet and break it into two pieces,
each piece will again have a North pole and a South
pole.
S N S N S N
Materials can be classified 3 ways
• Non Magnet:
– Will not attract a magnet or a ferromagnetic substance
– Glass, plastic, rubber or wood
– Work well as insulators for electrical wires
• Ferromagnet
– Not a magnet but something that can become magnetized by
hitting, heating, or touching it with a magnet OR by adding an
electrical charge (electromagnet)
– Is attracted by a magnet
– Must contain one of the following: iron, nickel or cobalt
– The magnetism can be turned on and off.
• Permanent Magnet
– can attract another magnet AND a ferromagnetic substance
Magnetic Fields
• Magnets produce magnetic forces and have magnetic
field lines
• The magnetic force is that force of attraction or repulsion
between magnets
• The magnetic field is the area of space in which the
magnetic force can work on another magnet
Mapping Magnetic Fields
• Rules:
– The magnetic field lines can never cross
– Always flow from North to South
– The closer the lines, the stronger the attraction
– The lines near the poles are closer to one another
because the poles have the greatest magnetic
intensity
Compass
– The needle of the compass is a small bar
magnet free to turn on a pivot
– Red (or any color) tip of the needle is
considered North and will always be attracted
towards its opposite the South
• Because the needle of a compass is a small magnet we
can use it to identify the poles of another magnets.
• When a compass is placed next to another magnet, the
north pole of the compass will point to the south pole of
the magnet (also indicating the direction of the magnetic
field lines)
Electromagnetism – straight line
conductor (AKA a wire)
• Electricity and Magnetism – how are they related?
• When an electric current passes through a wire a
magnetic field is formed.
• Have a North and a South pole
• They have a circular magnetic field
Straight Line Conductor – Right Hand
Rule
• Point your thumb in the direction of conventional current
(toward the negative terminal.)
• The direction that your fingers wraps around the wire
show the direction of the magnetic field lines -- the hand
may either be in front or behind, depending on where the
negative post is found
– These lines are circular
• Your fingernails always point South and your knuckles
point North If you place a compass near the wire, the
north pole of the compass will point in the direction of
your finger nails (the same direction as the arrows)
• South and North will be found above or below the
straight line conductor – NEVER at the ends
Because the field is
circular, the
direction of the
compass depends
on where the
compass is located
in relation to the
wire