Module 3.1 Magnetism

Magnetism:

Charges particles in motion exhibit magnetism

Magnetic Domain:

accumulation of many atomic magnets

Electron needs to be in _____ to display any kind of magnetism

motion

Magnetic materials are usually in a _________ state

non-magnetized

If domains align:

o  Results in a magnetized material with a North to South orientation

o   Effectively one N pole and one S pole

SI Units

Tesla (T)

Older SI Unit term

Gauss (G)

Classification of Magnets

1. Natural

2. Artificial Permanent

3. Electromagnets

Natural (Found in nature)

Earth is a dipole (has two poles N and S)

Example: Magnetite [lodestone or iron oxide (Fe₃O₄)]

Artificial Permanent  (manmade)

Hardened steel or alloy (alnico)

Example: Compass

Electromagnets (temporary)

Created by a current of e^- & iron core

Magnetic Permeability (Susceptibility)

ease with which material can be magnetized

Magnetic Retentivity

Ability of a material to hold magnetization

Permeability & Retentivity are _____ ______

inversely related

Magnetic Classification of Matter

1. Ferromagnetic

2. Paramagnetic

3. Diamagnetic

4. Nonmagnetic

Ferromagnetic

• Materials that can be magnetized

• Exhibit strong magnetic properties

• Are strongly attracted to a magnet

Paramagnetic

• Materials that are only weakly attracted to a magnetic field

• Loosely influenced by a magnetic field

Diamagnetic

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

Nonmagnetic

Materials unaffected by a magnetic field

Magnetic Force Field

Lines of force  (magnetic flux lines)

_____ outside the magnet

N → S

_____ inside the magnet

S → N

Field lines pass through both magnetic & nonmagnetic materials

concentrated by magnetic material

unaffected by nonmagnetic materials

Laws of Magnetism

1. Every magnet has two poles

2. Magnetic Laws

3. Analogous to Coulomb's laws

Every magnet has two poles

designated N & S

Magnetic Laws

Like poles repel, unlike poles attract

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.

Two poles have a magnetic charge of 4 T and 6 T each and they are placed 2 meters apart. What is the force between them?

4T x 6T = 24N

Two poles have a magnetic charge of 4 T and 6 T each and they are placed 2 meters apart. What if the poles were then moved to 1 meter apart?

Strength of Magnetism determined by the number of field lines per unit area

·         Strong fields = more lines of force

·         Strong field = closer lines of force

Is the Earth a strong of weak magnet?

Weak

How to Create a Magnet

1.      Stroking an iron bar repeatedly with a magnet

2.      Hammering a piece of iron in the presence of a magnet