(T) The system international (SI) unit of magnetic flux density. Definition: 1 T is the field intensity generating 1 N (newton) of force per ampere of current per meter of conductor. The tesla unit value is defined as a field strength of 1 weber per square meter of area, where 1 weber represents 1 x 10⁸ (100 000 000) flux lines. One T is equal to 10 000 gauss, the older (CGS) unit. A field of 1 tesla is quite strong, the Earth's magnetic flux density, at its surface, is about 50 microteslas (µT).

When a group of spins is placed in a magnetic field, each spin aligns in one of the two possible orientations. The relative numbers of spins with different alignments will be given by the Boltzmann distribution.
Definition: if a system of particles, which are able to exchange energy in collisions is in thermal equilibrium, then the relative number (population) of particles, N1 and N2, in two particular energy levels with corresponding energies, E1 and E2, is given by N1/N2 = exp [-(E1 - E2)/kT ] where k is the Boltzmann constant and T is the absolute temperature. For example, in NMR of protons at room temperature in a magnetic field of 0.25 tesla, the difference in relative numbers of spins aligned with the magnetic field and against the field is about one part in a million; the small excess of nuclei in the lower energy state is the basis of the net magnetization and the resonance phenomenon.

Material that allows heat or electric current to flow.

See also Semiconductor, Electric Field Strength, Electric Flux Density, Electromagnetic Lens, Tesla, and Thermal Units Per Hour.

Magnetic flux density is the amount of magnetic flux per unit area of a section, perpendicular to the direction of flux. The magnetic flux density is the product of the magnetic field strength and permeability. The SI unit for flux density is weber per square meter. One weber per square meter equals one tesla (T).