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Chapter 4

PHYSICS 1L03 Chapter Notes - Chapter 4: Inverse-Square Law, Flux, Alnico


Department
Physics
Course Code
PHYSICS 1L03
Professor
Christine Wilson
Chapter
4

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Electromagnetism
Magnetism
Orbital Magnetic Moment: when a charged particle is in motion, a magnetic
field perpendicular to the motion will be created.
Spin Magnetic Moment or Electron Spin: The magnetic effect created by
electrons spinning on their axes.
Magnetic Dipoles or Magnetic Domains: Groups of atoms with their net
magnetic field moving in the same direction.
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Magnetic Field: The force fields that are created when magnetic dipoles orient
to create a magnet; also called lines of flux and lines of force.
Lines of force always flow from north to south outside the magnet and from south
to north within a magnet.
Flux density: (1) A measure of the intensity of magnetization produced by a
magnetic field. (2) A vector quantity representing the number of flux lines
crossing a unit area at right angles. Measured in Tesla or Gauss
1 tesla = 10000 gauss, and
magnetic flux is a measure of the strength of a magnetic field over a given area,
measured in Weber
Types of Magnets
Natural Magnets: Created when iron oxide remains in the earth's magnetic
field for ages, slowly orienting the magnetic dipoles in the same direction.
Artificial Permanent Magnets: Manufactured from steel alloy called alnico,
composed of aluminum, nickel, and cobalt.
Electromagnets: Temporary magnet produced by moving electric current.
Laws of Magnetism
1. Repulsion-attraction: Like poles repel; unlike poles attract.
2. The inverse square law: Directly proportional to the product of the
magnitude and inversely proportional to the square of the distance between
them.
3. Magnetic Poles: Every magnet has two poles.
Magnetic Classification of Materials
Permeability is the ease with which a material can be magnetized.
Retentivity is the ability of a material to stay magnetized.
1. Ferromagnetic: A material with high magnetic permeability (imposes little
resistance to orientation in the presence of a magnetic field). Such materials as
iron, steel, and nickel are ferromagnetic substances.
2. Paramagnetic: Weakly attracted to magnetic fields.
3. Diamagnetic: Diamagnetism is a very weak form of magnetism that is only
exhibited in the presence of an external magnetic field. It is the result of changes
in the orbital motion of electrons due to the external magnetic field. The induced
magnetic moment is very small and in a direction opposite to that of the applied
field. When placed between the poles of a strong electromagnet, diamagnetic
materials are attracted towards regions where the magnetic field is weak.
4. Nonmagnetic: Materials not affected by a magnetic field and cannot be
magnetized.
Electromagnetism
A moving charge produces a magnetic field.
Current Carrying Wire Applet
Oersted Experiment
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