ch36_esit

=Magnetism=

36.1 Magnetic Poles
Magnetic forces and electric charges are alike in many ways. They both attract and repel while never touching, depending on which end is held near the other, and the strength of the forces depend on the distance between the two magnets. These magnetic forces are produced by **magnetic poles**. All magnets have two poles; a north-seeking pole, and a south-seeking pole. The north-seeking pole always points northward, and the sout-seeking pole always points to the south. These poles are simply called the north and south poles, for short, and they are always located at both opposite ends of a magnet. >> **Like poles repel; opposite poles attract**

Although there are many similarities between magnetic and electrical forces, there is one key difference. Unlike electrical forces, magnetic forces can never be isolated. In other words, there can never be a north pole without the presence of a south pole, and vice versa. Because of this, when you break a magnet in half, it will now create two whole magnets with north and south poles at each end.

36.2 Magnetic Fields[[image:field_lines.jpg width="161" height="141" align="right" caption="www.phys.lsu.edu"]]
The area around a magnet in which a magnetic force is exerted is called a **magnetic field**. Magnetic fields can be shown through //magnetic field lines//. These magnetic field lines show the direction and shape of the magnetic field around the magnet. The lines curve around the magnet, always beginning at the north pole and ending at the south pole. The magnetic field strength is greater where the field lines are closer, and is also greater at the poles of the magnet.

36.3 The Nature of a Magnetic Field
Magnetic fields can be produced when any time eletrical charges are in motion. The electron are always in motion but the reason everything isn't magnetized is because the electrons cancell each other out in most cases.

36.4 Magnetic Domains
Magnetic Domains- Atoms that group together into clusters that all have the same magnetic orientation. When iron is unmagnetizded the domains are randomly organized and cancel each other out.When the iron begins to become magnetized the domains become aligned and start to constructively interfere. When the iron is strongly magnetized almost all of the domains will have the same orientation. Once an object is magnetized by aligning its magnetic domain, if the magnet is broken each part will have two equally strong poles.

36.5 Electric Currents and Magnetic Fields
All electric currents have a magnetic field around them created by their motion. Electromagnet- is a current carrying coil of wire with many loops. These are mainly used in junk yards to big up large amount of metal in a short amount of time. When current carrying wires are bent into loops the magnetic field increases in intensity.

36.6 Magnetic Forces on Moving Charged Particles
When a charged particle moves through a magnetic field in any direction other than parallel to the field the particle will feel a force from the magnetic field. The force becomes the greatest when the particles move perpendicular to the magnetic field lines. This property is used in TV to guide a beam of electrons to strike the correct colored dots on the screen.

36.7 Magnetic Forces on Current Carrying Wires
If the moving charges are in a wire then they will transfer the force to the wire causeing the wire to also move. The direction of the force is always sideways.

36.8 Meters to Motors
Electric meters can be made by wrapping a coil of wire around a magnet. There is a force caused by the current passing through the coil of the magnet, which causes a needle to move on the scale. When the cirvuit is varied, the instrument can be able to read either current, voltage, or resistance. The sensitive current-indicating instrument is called a **galvanometer**. It is also possible for these meters to be made into motors, which transform electrical energy into mechanical energy.

36.9 The Earths Magnetic Field
The earth in itself is essentially an extreme large magnet. It is composed of two poles, a north and south pole, just like any other magnet. The north pole is actually a south seeking pole, and the south pole is actually a north seeking pole. This is why compass' will always point toward the north pole. The current theory on why the earth is magnetized is because of the earth's molten interior that creates a convection current which in turn magnetizes the earth.