RADT 142 - Magnetism

Magnetism

Charged particles in motion exhibit magnetism

magnetic domain

accumulation of many atomic magnets

Nature of Magnetism

Magnetic materials are usually in a non magnetized state

-domains in random arrangement

If domains align

-results in a magnetized material with a N to S orientation

-effectively one N pole and one S pole

S.I. unit of magnetism

Tesla (T)

Gauss (G)

Classification of Magnets

NATURAL (found in nature)

ARTIFICIAL PERMANENT (man made)

ELECTROMAGNETS (temporary)

natural magnet

-Earth is a dipole

-Magnetite [lodestone or iron oxide (Fe3O4)]

•natural ore that exhibits magnetism

Artificial Permanent Magnets

-Hardened steel or alloy (alnico)

-Compass

electromagnets (temporary)

Created by a current of e- & iron core

magnetic permeability (susceptibility)

the ease with which a material can be magnetized

Magnetic Retentivity

ability of a material to hold magnetization

relationship between permeability and retentivity

Permeability & Retentivity -- inversely related

Magnetic Classification of Matter

Ferromagnetic Materials

Paramagnetic Materials

Nonmagnetic Materials

Diamagnetic Materials

Ferromagnetic Materials

-Materials that can be magnetized

-Exhibit strong magnetic properties

-Are strongly attracted to a magnet

Paramagnetic materials

-Materials that are only weakly attracted to a magnetic field

-Loosely influenced by a magnetic field

nonmagnetic materials

-Materials unaffected by a magnetic field

Diamagnetic materials

-Diamagnetic materials are weakly repelled by a magnetic field. These materials cannot be magnetized and are not attracted to a magnet.

-Most elements in the periodic table, including copper, silver, and gold, are diamagnetic.

Magnetic Force Field

•Lines of force (magnetic flux lines)

•Direction

-N to S outside the magnet

-S to N inside the magnet

Form a closed loop

magnetic field

Field lines pass through both magnetic & non magnetic materials

-concentrated by magnetic materials

-unaffected by non magnetic materials

Laws of Magnetism

1. Every magnet has two poles, designated N & S

2. Like poles repel

unlike poles attract

3. Analogous to Coulomb's laws

-The force between two magnetic poles varies directly as the strength of the poles and inversely as the square of the distance between poles.

Strength of Magnetism determined by

# of field lines per unit area