Magnetism Fundamentals

• The Earth's north magnetic pole has south polarity.
• Early natural magnets were known as lodestones.
• Two south poles of magnets will repel each other.
• The polarity of an electromagnet can be determined using the right-hand rule if the direction of current flow is known.

Definitions

• Flux Density: A measure of the strength of a magnetic field, expressed as the amount of magnetic flux per unit area.
• Permeability: The measure of a material's ability to support the formation of a magnetic field.
• Reluctance: The opposition to magnetic flux in a magnetic circuit.
• Saturation: The state where an increase in magnetizing force produces little or no increase in magnetization.
• Coercive Force: The intensity of the magnetic field required to reduce the magnetization of a material to zero after it has reached saturation.
• Residual Magnetism: The magnetism remaining in a material after the magnetizing force is removed.

Classifications of Magnetic Materials

• Ferromagnetic: Strongly attracted to magnetic fields and can be easily magnetized (e.g., iron, nickel, cobalt).
• Paramagnetic: Weakly attracted to magnetic fields (e.g., aluminum, magnesium).
• Diamagnetic: Weakly repelled by magnetic fields (e.g., copper, silver).

Electromagnet Strength

• The strength of an electromagnet is determined by the number of turns in the coil, the current flowing through the coil, and the permeability of the core material.

Natural Magnets

• Three substances that form natural magnets are magnetite, pyrrhotite, and franklinite.

Core Material

• A ferromagnetic core material can be used to increase the strength of a magnetic field.

Demagnetization Methods

• Three ways to demagnetize an object are heating it above its Curie temperature, subjecting it to an alternating magnetic field that gradually decreases in amplitude, and physically shocking or hammering it.