24-1 Magnets: permanent & temporary

General Properties Hang the bar magnet from the thread, observe what happens……. Positions itself in the N-S directions - magnet is polarized Has two ends – North seeking and South seeking A compass is a small magnet free to turn

General Properties Observe what happens when another magnet is brought to the different sides of the magnet The two N poles repel as the two S poles N and S pole attract All magnets have two singular poles or Monopoles When magnet is broken in half, magnets orient themselves in a N & S direction

Simple Magnets Touch a magnet to a piece of metal (iron nail) and try to pick up paper clips along the nail Nail has become polarized (temporarily) Either end of a magnet will attach to a metal

Permanent Magnets Made of ALNICO V Aluminum – Nickel – Cobalt – and other rare earth elements

Magnetic Field Magnets are a long range force Invisible “lines” surround the magnet showing the magnetic field Number of magnetic lines is magnetic flux # of lines is proportional to strength Concentrated at the poles Lines flow out of the N and into the S in closed loops

Electromagnetism Electric currents through a wire create a magnetic field perpendicular to the current First Right hand Rule Direction of current  Thumb Direction of magnetic field  Fingers coiled

Magnetic Field near a Coil A wire looped several times to form a coil and a current is allowed to flow, the field around all the loops is always in the same direction Solenoid Long coil wire consisting of many loops

Magnetic Field near a Coil When there is an electric current in a coil wire, the field acts like a permanent magnet Electromagnet Strength of the field is proportional to the current in the coil Increasing the number of loops increases the strength

Electromagnet Strength can also be increased by adding an iron rod inside the coil Field will magnetize the rod Second right hand rule Direction of magnetic field produced by an electromagnet Curl fingers around loops in the direction of the current Thumb is the North pole of the magnet

Magnetic Domains Each electron in an atom acts like a tiny electromagnet  generally in three magnetic elements Iron, nickel, & cobalt Groups of electrons are known as domains Shown as arrows that are random in direction Once a magnetic field is present, arrows aligned and become magnetized

Physics and Earth Science Iron is found in the oceanic rocks as basalt As ocean floor spreads, magma is released Overtime, earth’s magnetic field has changed