After static charges and steady circuits, we enter one of the most fascinating phenomena of electromagnetism: magnetism. Electricity and magnetism are in fact two sides of the same coin, a discovery that took more than a century and culminated in Maxwell’s equations. This chapter introduces the magnetic field , the Lorentz force on moving charges, the Laplace force on wires, the sources of the field (wire, conducting plane, solenoid), Ampère’s law, the loop as a magnetic dipole and the electric motor, closing with the Hall effect.
Historical context — Ørsted, 1820
Until the early nineteenth century, electricity and magnetism were considered separate phenomena. In 1820, during a lecture, the Danish physicist Hans Christian Ørsted noticed by chance that a compass needle placed near a current-carrying wire deflected abruptly: the first experimental proof that electric currents produce a magnetic field, and the birth of electromagnetism.
Sections
- Analogy with the electric field
- Magnetic field lines
- Lorentz force
- Magnetic field produced by a current
- Laplace force on a wire
- Magnetic field of a conducting plane
- Loop as a magnetic dipole and electric motor
- The Hall effect
Reflections
- Magnetism is electrostatics plus relativity
- Why the magnetic force does no work (and why that is not a paradox)