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!)