Part of MAG-01 — Magnetic Effects of Current & Magnetism

Definitions Glossary — 18 Key Terms

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TermDefinitionUnit / Dimensional Formula
Magnetic Field (B)The region around a magnet or current where magnetic forces act; defined by force on a moving charge F = qv×BTesla (T); [MT^{-2}$$A^{-1}]
Biot-Savart LawdB = (μ_{0}/4π)(I dl sinθ/r2r^{2}); gives magnetic field due to a current element; magnetic analog of Coulomb's law[MT^{-2}$$A^{-1}]
Ampere's Circuital Law∮B·dl = μ_{0}I_enc; line integral of B around any closed loop equals μ_{0} × enclosed current[MLT^{-2}$$A^{-1}]
Permeability of Free Space (μ_{0})4π × 10^{-7} T·m/A; fundamental constant relating B to the current producing it[MLT^{-2}$$A^{-2}]
Lorentz ForceF = q(E + v×B); total electromagnetic force on a charge q moving with velocity vNewton (N); [MLT2LT^{-2}]
Magnetic Moment (M)M = NIA for a current loop; measure of loop's tendency to align with an external fieldm2m^{2}; [AL2AL^{2}]
Torque on a Current Loopτ = NIAB sinθ = MB sinθ; torque experienced by a magnetic moment in an external fieldN·m; [ML^{2}$$T^{-2}]
SolenoidA long cylindrical coil with N turns and length L; creates uniform B = μ_{0}nI inside
ToroidA donut-shaped solenoid; B = μ_{0}NI/(2πr) inside ring; B = 0 in hollow centre and outside
Cyclotron Radiusr = mv/(qB); radius of circular path of a charged particle in uniform Bm; [L]
Cyclotron PeriodT = 2πm/(qB); time for one complete revolution; independent of speeds; [T]
Magnetic Susceptibility (χ)χ = M/H; dimensionless measure of how much a material magnetises in response to HDimensionless
Relative Permeability (μᵣ)μᵣ = 1 + χ; ratio of material's permeability to μ_{0}; dimensionlessDimensionless
Diamagnetismχ < 0; material is weakly repelled by external field; examples: Cu, Bi, H2OH_{2}O
Paramagnetism0 < χ << 1; material weakly attracted; obeys Curie's law χ = C/T
Ferromagnetismχ >> 1; strongly attracted; has magnetic domains; shows hysteresis
RetentivityResidual magnetic flux density (B) retained when external field H is reduced to zeroTesla (T)
CoercivityMagnitude of reverse H required to reduce residual B to zero; [A/m]A/m; [L1L^{-1}A]

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