ch21_pm

=CHAPTER 21=

Section 1
Every magnet has two magnetic poles, a north and south pole. Every magnet can be broken in two and each part will still have a north and south pole. Unlike magnets attract and like magnets repel each other. A magnetic dipole, which is a pair of magnetic poles, creates a magnetic filed around it and interacting with other magnetic dipoles in the vicintity. The magnetic field strength (B) is measured in tesla (T). The direction of magnetic fields is seen as the direction a north pole would face if the magnet were placed in the magnetic field. When the magnetic field lines are drawn they are drawn as arrows that lay on the plane of the paper. If they are coming out of the page, they are seen as dots, and if they are going into the page they are seen as a bunch of "x"s. Picture it as if an arrow were shot, if it comes to you, then it is only the point you see, if it is shot away from you, it is the feathers you see. Interestingly enough, the magnetic north pole is actually the geographic south pole and vice versa on earth.

Section 2
A magnetic field exists around any current-carrying wire, the direction follows the right hand rule- point your thumb of your right hand in the direction of the current and wrap your fingers inwards, the direction follows your fingers. A magnetic field created by a solenoid or coil is similar to the magnetic field of a permanent magnet, where the direction is still determined by the right hand rule. Magnetic domain is a group of atoms whos fields are all aligned. Some materials just will not magnetize whereas others will always stay partially magnetized after they are intially magnetized. Whenever any material becomes magnetized, all of the domains in the material are oriented in the same domain. Materials that are easily magnitized will go back to a random distribution once the external field is removed, but ones that are not easily magnetized will remain partially magnetized after the external field is removed.

Charged Particle in a Magnetic Field
=== When a charge moves through a field, a force will be exerted by the field on the charge. This force is at a maximum when the charge moves perpendicular to the field and is at zero when it moves along the filed lines. === math \displaystyle B=\frac{F_{mag}}{qv} math === Q is the moving charge and v is its velocity. The direction fof the force on a positive charge through the field can be found once again using the right hand rule. If the charge is a negative one, then simply find the way a positive charge would go, and reverse it. If a particle is moving perpendicular to the magnetic field, the particle will move in a circular path. If the particle is not moving perpendicularly, then the particle will move in a helical path, not a circular one. ===

When there is a length of wire, L, with an external magnetic force, B, carrying a current, I, undergoes a magnetic force of
math \displaystyle F_{magnetic}=BIL math