Chapter 21 - Physics Notes

Law of Magnetic Poles: The law stating that unlike poles attract and like poles repel.
Magnetic Field: The region around a magnet where magnetic materials and moving charges experience a magnetic force.
Magnetic Field Lines: Lines indicating the direction a magnetic north monopole would travel, aligning with the magnetic field.
Magnetic Flux Density (B): The strength of the magnetic field at a point, measured in teslas (T). 1 tesla = 1 volt-second per square meter.
Ferromagnetic Material: A material that can be permanently magnetized, with strong atomic magnetic dipole moments.
Domain: Tiny regions of a material where the magnetic moments of its atoms are aligned.

Historical Background

The Chinese discovered that natural magnets suspended by a string rotate until one end points north.
De Maricourt identified magnetic poles and their properties of attraction and repulsion.
William Gilbert concluded that Earth acts as a giant magnet.

Magnets always exist as dipoles (no monopoles in nature).
Magnetic field lines are closer at poles, indicating stronger fields.
Magnetic fields are three-dimensional and described by the magnetic field vector (B).

Magnetic fields arise from electric currents (Ampère's Law).
Unpaired electrons in atomic energy levels create a material's magnetic dipole moment (μ).
Ferromagnetic materials can retain magnetism, while paramagnetic materials lose it after the external field is removed.
Diamagnetic materials develop magnetism in the opposite direction of an external field.

Earth's magnetic poles are not aligned with geographic poles and drift over time.
The magnetosphere contains Earth's magnetic field, distorted by solar winds.
The magnetosphere protects life by trapping solar wind particles and creating auroras (e.g., northern lights).