Magnetic field strength is a measure of how intense a magnetic field is at a given point. It determines the force a moving charged particle experiences, the torque on a magnetic dipole, and the energy density stored in the field. In practical terms, it tells you how strongly a magnet will attract a paperclip or how much a particle's path will bend in a particle accelerator.
History
The concept evolved from early observations of lodestones and compass needles. The quantitative description was developed in the 19th century, with key contributions from André-Marie Ampère, who studied the forces between current-carrying wires, and James Clerk Maxwell, who unified electricity and magnetism in his equations in the 1860s.
How it works
The strength is typically quantified as a vector field, with both magnitude and direction. In the SI system, it is measured in teslas (T), where one tesla is one newton per ampere-meter. The force on a moving charge is given by the Lorentz force law, F = qv × B, where B is the magnetic flux density (often used interchangeably with field strength in most contexts). The field arises from moving charges, such as electric currents in wires or the intrinsic spin of electrons in magnetic materials.
In practice
Magnetic field strength is essential in designing MRI machines, particle accelerators like the LHC, and magnetic storage devices. It is also used in geophysics to map underground structures and in space missions to measure planetary magnetic fields.
Fun fact
The strongest magnetic field ever produced in a laboratory is about 1,200 teslas, created using an explosive technique called flux compression, which is strong enough to distort the shape of atoms.
Units by system: SI: t · CGS: g · Planck: b p · natural: ev2
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