Describe the properties of a magnetic field.

• A magnetic field is a vector field that can be used to determine the magnetic force exerted on moving electric charges, electric currents, or magnetic materials.
• Magnetic fields can be produced by magnetic dipoles or combinations of dipoles, but never by monopoles.
• Magnetic dipoles have north and south polarity.
• A magnetic field is a vector quantity and can be represented using vector field maps.
• Magnetic field lines form closed loops.
• Magnetic fields in a bar magnet form closed loops, with the external magnetic field pointing away from one end (defined as the north pole) and returning to the other end (defined as the south pole).

Describe the magnetic behavior of a material as a result of the configuration of magnetic dipoles in the material.

• Magnetic dipoles result from the circular or rotational motion of electric charges. In magnetic materials, this can be the motion of electrons.
• Permanent magnetism and induced magnetism are system properties that both result from the alignment of magnetic dipoles within a system.
• No magnetic north pole is ever found in isolation from a south pole. For example, if a bar magnet is broken in half, both halves are magnetic dipoles.
• Magnetic poles of the same polarity will repel; magnetic poles of opposite polarity will attract.
• The magnitude of the magnetic field from a magnetic dipole decreases with increasing distance from the dipole.
• A magnetic dipole, such as a magnetic compass, placed in a magnetic field will tend to align with the magnetic field.
• A material’s composition influences its magnetic behavior in the presence of an external magnetic field.
• Ferromagnetic materials such as iron, nickel, and cobalt can be permanently magnetized by an external field that causes the alignment of magnetic domains or atomic magnetic dipoles.
• Paramagnetic materials such as aluminum, titanium, and magnesium interact weakly with an external magnetic field, in that the magnetic dipoles of the material do not remain aligned after the external field is removed.
• All materials have the property of diamagnetism, in that their electronic structure creates a usually weak alignment of the dipole moments of the material opposite the external magnetic field.
• Earth’s magnetic field may be approximated as a magnetic dipole.

Describe the magnetic permeability of a material.

• Magnetic permeability is a measurement of the amount of magnetization in a material in response to an external magnetic field.
• Free space has a constant value of magnetic permeability, known as the vacuum permeability μ₀, that appears in equations epresenting physical relationships.
• The permeability of matter has values different from that of free space and arises from the matter’s composition and arrangement. It is not a constant for a material and varies based on many factors, including temperature, orientation, and strength of the external field.

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Simulation page: Magnet and Compass