Magnetism Magnetism originates at the atomic level and is caused by moving electric charge Magnetic objects: Create magnetic fields around themselves Exert magnetic forces on other magnets, ferromagnetic materials, moving electric charges Electric fields and forces are created by static (non-moving) electric charges Magnetism and electrostatics are two sides of same coin – electromagnetism

Magnetic Materials Ferromagnetic materials have magnetic domains Magnetic domains are microscopic regions within a material in which the magnetic fields of individual atoms are aligned In a non-magnetic object, the domains are randomly aligned, cancelling each other out In a permanent magnet, the domains are uniformly aligned, reinforcing each other In “soft” magnetic materials, domains can be temporarily realigned by an external magnetic field

Magnetic Domains

Magnetic Fields and Forces As with electric fields, magnetic fields have a direction and depend on distance Magnetic field lines are drawn as arrows that go out of the North Pole of a magnet and into the South Pole of a magnet closer spacing = stronger field As with electric forces, magnetic forces are both attractive and repulsive Unlike magnetic poles (N & S) attract Like magnetic poles (N & N or S & S) repel

Magnetic Field Lines

Electromagnetism Electromagnetism is the magnetism that results from an electric current moving through a wire The direction of the current determines the direction of the magnetic field The direction of a magnetic field around a current-carrying wire is given by a right-hand rule Thumb points in the direction of current Fingers point in the direction of magnetic field

Electromagnetism

Force on a Wire with Current If a current-carrying wire is placed in a magnetic field, a force is exerted on the wire The direction of force is perpendicular to both the direction of the current and the direction of the magnetic field The three directions are given by another right-hand rule Thumb = direction of current Fingers = direction of magnetic field Open palm = direction of force

Force on a Wire with Current

Solenoids and Electromagnets Solenoids are coils of current-carrying wire that exert a magnetic field The strength of the field depends on the number of loops in the coil and the amount of the current Electromagnets are solenoids with a core of ferromagnetic material The magnetic field from the coil aligns the domains in the core, further strengthening the magnetic field

Solenoids

Electromagnets