ch36_esjp

**Chapter 36 - Magnetism**

__Sections:__ 
 * 1) Magnetic Poles
 * 2) Magnetic Fields
 * 3) The Nature of a Magnetic Field
 * 4) Magnetic Domains
 * 5) Electric Currents and Magnetic Fields
 * 6) Magnetic Forces on Moving Charged Particles
 * 7) Magnetic Forces on Current-Carrying Wires
 * 8) Meters to Motors
 * 9) The Earth's Magnetic Field
 * //Chapter 36 Section 1 - Magnetic Poles//**

 The strength of the interaction between magnets depends on the distance *magnets can be broken in half, and result in two new magnets; each with a north and south pole.
 * __magnetic poles-__ regions on a magnet that produce magnetic forces.
 * It is important to remember that like poles repel (north and north) and opposite poles attract (north and south)
 * <span style="font-family: Georgia, serif;">A difference between electric charges and magnetic poles is that electric charges can be isolated, and magnetic poles cannot.
 * <span style="font-family: Georgia, serif;">This is because the poles depend on each other, and a north pole cannot exist if there is no south pole.
 * <span style="font-family: Georgia, serif;">It is because the electrons do not need to be accompanied by protons
 * <span style="font-family: Georgia, serif;">north-seeking pole- the end that points northward on a compass.
 * <span style="font-family: Georgia, serif;">south-seeking pole- the end that points southward on a compass.


 * //Chapter 36 Section 2 - Magnetic Fields//**

<span style="font-family: Georgia, serif;">
 * <span style="font-family: Georgia, serif;">__magnetic field-__ a force field that fills the space around every magnet or current-carrying wire. Another magnet or current-carrying wire introduced into this region will experience a magnetic force.
 * <span style="font-family: Georgia, serif;">magnetic field lines- these spread out from one pole, curve around the magnet, and return to the other pole.


 * <span style="font-family: Georgia, serif;">The direction of the field lines of a magnet always go from the south pole to the north pole.
 * <span style="font-family: Georgia, serif;">Also, the closer the lines are in the field, than the stronger the magnet.
 * <span style="font-family: Georgia, serif;">This is why the lines are closer together towards the ends of the north and south pole rather than in the middle of the magnet.

<span style="font-family: Georgia, serif;"> //**Chapter 36 Section 3 - The Nature of a Magnetic Field**//

~ Magnetism is related to electricity. ~ A magnetic field is produced by the motion of electric charge and since motion is relative, the magnetic field is relative as well. ~ Both the orbital motion and the spinning motion of every electron in an atom produce magnetic fields. These fields combine constructively or destructively to produce the magnetic field of the atom. The resulting field is greatest for iron atoms.



//**<span style="font-family: Georgia, serif;">Chapter 36 Section 4 - Magnetic Domains **//


 * <span style="font-family: Georgia, serif;">__magnetic domains-__ microscopic clusters of atoms with their magnetic fields aligned.
 * <span style="font-family: Georgia, serif;">These domains are iron atoms that are so strong that they tend to align with each other
 * <span style="font-family: Georgia, serif;">The magnetic domains are microscopic
 * <span style="font-family: Georgia, serif;">Because domains are rotated when they become aligned in the presence of a strong magnet, often when the magnet is taken away, they will return to their original position.
 * <span style="font-family: Georgia, serif;">This does not occur when permanent magnets are made with soft iron (which is easier to magnetize)
 * <span style="font-family: Georgia, serif;">Although they are permanent by design, or by stroking iron with another magnet, they can also be weakened by dropping them or heating them.

<span style="font-family: Georgia, serif;">**//<span style="font-family: Georgia, serif;">Chapter 36 Section 5 - Electric Currents and Magnetic Fields //**

<span style="font-family: Georgia, serif;">~ The magnetic field that surrounds a current-carrying conductor can be demonstrated by arranging an assortment of magnetic compasses around a wire and passing a current through it. ~ The compasses line up with the magnetic field produced by the current and show it to be a pattern of concentric circles about hte wire. ~ When the current reverses direction, the compasses turn completely around, showing that the direction of the magnetic field changes also. <span style="font-family: Georgia, serif;">~ SEE ELECTROMAGNETS ARE COOOOLL!
 * <span style="font-family: Georgia, serif;">__electromagnet-__ magnet with a field produced by electric current; usually in the form of a wire coiled around a piece of iron.

//**Chapter 36 Section 6 - Magnetic Forces on Moving Charged Particles**//

>>
 * <span style="font-family: Georgia, serif;">If a charged particle moves in a magnetic field, the magnetic character of its motion becomes evident.
 * <span style="font-family: Georgia, serif;">When the particle moves, it experiences a deflecting force, and is greatest when it is moving perpendicular to the magnetic field lines.
 * <span style="font-family: Georgia, serif;">The force acually reaches zero when it is parallel to the magnetic field lines.
 * <span style="font-family: Georgia, serif;">The direction of force is perpendicular to both the magnetic field lines and the velocity of the charged particle
 * <span style="font-family: Georgia, serif;">This explains why it is deflected when it crosses the field lines, but not when it is parallel
 * <span style="font-family: Georgia, serif;">This force is unique in that it does not act in a direction between sources, but instead perpendicular to magnetic field and velocity. [[image:http://dev.physicslab.org/img/fee67699-19ec-46f7-bb73-55ef330b982c.gif width="133" height="175" align="center" caption="rightvelocity.gif (1829 bytes)"]]

<span style="font-family: Georgia, serif;">**//<span style="font-family: Georgia, serif;"><span style="font-family: Georgia, serif;"> Chapter 36 Section 7 - Magnetic Forces on Current-Carrying Wires //**

~ Simple logic tells you that if a charged particle moving through a magnetic field experiences a deflecting force, then a current of charged particles moving through a magnetic field also experiences a deflecting force. ~If the direction of current in the wire is reversed, the deflecting force acts in the opposite direction.


 * So answer this one: What law of physics tells you that if a current-carrying wire produces a force on a magnet, a magnet must produce a force on a current-carrying wire?
 * Answer: Newton's Third Law, which applies to ALL forces of nature.

<span style="font-family: Georgia, serif;">**//Chapter 36 Section 8 - Meters to Motors//**

<span style="font-family: Georgia, serif;">
 * <span style="font-family: Georgia, serif;">__galvanometer__- a sensitive current-indicating instrument. When an electric current passes through the coil, each loop produces its own effect on the needle so that a very small current can be detected.
 * <span style="font-family: Georgia, serif;">__ammeter__- when a galvanometer is calibrated to measure current (amperes).
 * <span style="font-family: Georgia, serif;">__voltmeter__- when a galvanometer is calibrated to measure electric potential (volts).
 * <span style="font-family: Georgia, serif;">__brushes__- the parts of the wire that brush against stationary contacts on the shaft of a dc motor.
 * <span style="font-family: Georgia, serif;">__armature__- an iron cylinder that rotates when energized with electric current and is wound with many loops of wire.

<span style="font-family: Georgia, serif;">//**Chapter 36 Section 9 - The Earth's Magnetic Field**//

<span style="font-family: Georgia, serif;">The earth itself is a huge magnet, and therefore has a north pole and a south pole. <span style="font-family: Georgia, serif;">The magnetic field of the earth can be explained by examining the molten iron core of the earth.
 * <span style="font-family: Georgia, serif;">This means that compasses that are attracted to the magnetic north pole do not actually point north.
 * <span style="font-family: Georgia, serif;">__magnetic declination__- the discrepancy between the orientation of a compass and true north.
 * <span style="font-family: Georgia, serif;">Some believe that the moving charges going around the earth create the magnetic field
 * <span style="font-family: Georgia, serif;">Others argue that the currents of the heat from the core cause the magnetic field (due to the release of nuclear energy in the form of heat, and radioactive decay combined with the earth's rotation)
 * <span style="font-family: Georgia, serif;">The earths poles are not permanent, and eveery 7oo,000 years or so, the poles switch with each other

//**Practice Problems**//

<span style="font-family: Georgia,serif;">The following practice problems were assigned by Mr. Strong and are found in the textbook:

<span style="font-family: Georgia, serif;">Pages 575-576 Review Questions #1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 15, 19 Page 576 Think and Explain #1, 2, 3, 4, 5, 6, 7, 8

//**Sources**//

<span style="font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">Conceptual Physics: Third Edition with Expanded Technology by Paul G. Hewitt
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