MAGNETIC FORCES Magnetism & Fields

M AGNETISM  Law of magnetism states that like magnetic poles repel and unlike poles attract each other.

M AGNETIC F IELD  Magnets exert forces that seem to originate from the magnetic poles, and they can affect another magnetic object even without contact.  The ancient Greeks called this effect “ action at a distance.”  Field lines are “lines of force”

M AGNETIC F IELD L INES

M AGNETIC F IELD Magnetic field lines have the following properties:  magnetic field lines are continuous loops that never cross  inside the magnet, the magnetic field lines point from the south pole to the north pole  outside the magnet, the magnetic field lines point away from the north pole toward the south pole  the closeness of the lines represents the strength of the magnetic field (the closer the lines are together, the stronger the magnetic field)  if the field lines are parallel, the magnetic field is uniform

M AGNETIC F IELD L INES

M AGNETIC F IELD 1 Tesla = 1 T = 1 N / (A*m)

D OMAIN T HEORY  A material that is made from a magnetized material and creates a magnetic field is a permanent magnet.  Some materials become magnetized when they are placed in an external magnetic field. These are called ferromagnetic materials, and include iron, nickel, and cobalt.

D OMAIN T HEORY  The outermost electrons of the atoms of ferromagnetic materials create tiny magnetic fields in each atom.  The magnetic fields of adjacent atoms can align to reinforce each other, forming small regions, or domains, with intense magnetic fields.

M AGNETISM AND C URRENT  Early scientists believed that electricity and magnetism were related, but the link between them eluded scientists until 1820  Oersted’s principle: When a current moves through a conductor, it creates a magnetic field.

R IGHT H AND R ULE  It was shown that when a current flows in a straight conducting wire, the magnetic field forms a circular pattern that is perpendicular to the wire

S OLENOID (C OIL )  The magnetic field of a solenoid is similar to a bar magnet

S OLENOID (C OIL )

M AGNETISM