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MAGNETISM AND
ELECTROMAGNETISM
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• 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!
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• 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.
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• 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
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• All magnets have a north pole and a south pole
• Like poles repel. Unlike poles attract
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• A compass needle is a small bar magnet that can freely rotate
• A compass needle always points north, or rather is
north-seeking
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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).
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MAGNETIC DOMAINS
• Microscopic groups of atoms with aligned magnetic poles
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MAGNETIC MATERIALS• Materials in which the domains will line
up in order to form a magnetic field
• Examples: iron, cobalt, and nickel
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WHAT HAPPENS WHEN YOU CUT A MAGNET IN HALF?
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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.
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• The domains of temporary magnets are only aligned when the material is influenced by a magnetic field. (ex. Refrigerator, white board)
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• 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
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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
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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!)