Download Magnetism - Midland ISD

MAGNETISM
AND
ELECTROMAGNETISM
• Magnetism = the phenomenon of
physical attraction for iron
observed in magnets, inseparably
associated with moving electricity
and characterized by fields of force
Magnetic force increases as magnets
move closer together!
• A magnetic field surrounds a
magnet and is strongest at the
poles; it is produced by the motion
of electric charge.
• Both the orbital & spinning motion
of every electron in an atom
produce magnetic fields.
• Magnetic field lines: arrows drawn from
north to south poles representing the
magnetic field.
• Number of field lines indicates the
relative strength of the magnet
• All magnets have a north pole and
a south pole
• Like poles
repel.
Unlike poles
attract
• A compass needle is a small bar
magnet that can freely rotate
• A compass needle always points
north, or rather is
north-seeking
INTERESTING FACT…
• The northern lights (aurora
borealis) & southern lights (aurora
australias) are results from the
interaction between the solar wind
and earth’s magnetic field (makes
the air glow
).
MAGNETIC DOMAINS
• Microscopic groups of atoms with
aligned magnetic poles
MAGNETIC MATERIALS
• Materials in which the domains will line
up in order to form a magnetic field
• Examples: iron, cobalt, and nickel
WHAT HAPPENS WHEN YOU CUT A MAGNET IN
HALF?
PERMANENT MAGNETS
• Material that keeps its magnetic
properties, even when it is not close to
other magnets
• Made by placing a magnetic material in
a strong magnetic field, which causes
the domains to remain aligned.
• The domains of temporary
magnets are only aligned when
the material is influenced by a
magnetic field. (ex. Refrigerator,
white board)
• Electromagnet – temporary magnet that is
created by electric current flowing in a
wire, usually in the form of a wire coiled
around a piece of iron
Magnetic field is
present only when
current is flowing
in the wire coil
Strength of an electromagnet depends
on three factors:
•
amount of current in the wire
•
amount of iron or steel in the core
•
number of turns in the coil
PRODUCING ELECTRIC CURRENT
• Electromagnetic induction – the production
of an electric current by moving a loop of
wire through a magnetic field or moving a
magnet through a wire loop (which changes
the magnetic field near the conductor; no
battery!)