Browse All 842 Physics Terms A–Z

Magnetic Dipole Electromagnetism & Electronics A·m² (or J/T) The basic magnetic structure created by a closed circulating current loop or intrinsic particle spin, possessing North and South magnetic poles. μ = I A, τ = μ × B

Magnetic Dipole Moment Electromagnetism & Electronics A·m² (or J/T) A vector quantity determining the torque experienced by a magnetic dipole when placed in an external magnetic field. μ = I A, U = -μ · B

Magnetic Domains Condensed Matter & Materials Physics μm to mm (Domain Size) Microscopic regions within a ferromagnetic material where atomic magnetic moments are aligned parallel in a uniform direction. Domain Wall Energy E_total = E_exchange + E_anisotropy

Magnetic Field Electromagnetism & Electronics T (Tesla = N/(A·m)) A vector field generated by moving electric charges, electric currents, or intrinsic magnetic moments that exerts magnetic forces on other moving charges and dipoles. F_mag = q (v × B), B = μ₀ I / (2π r)

Magnetic Flux Electromagnetism & Electronics Wb (Webers = T·m²) The measure of the total magnetic field passing normally through a specified surface area. Φ_B = ∫ B · dA = |B| |A| cos θ

Magnetic Helicity & Taylor Relaxation Plasma Physics Wb² (Magnetic Helicity Units) A topological invariant measuring the linking, twisting, and tangling of magnetic flux lines in a closed plasma volume. K = ∭ A · B dV, ∇ × B = μ B (Taylor State)

Magnetic Hysteresis Electromagnetism & Electronics J/m³ (Joules per cubic meter) The lagging of magnetization behind the applied magnetizing field in ferromagnetic materials during cyclic magnetization. Hysteresis Loss Area = ∫ H dB

Magnetic Mirror Plasma Physics Dimensionless Mirror Ratio B_max / B_min A magnetic confinement configuration where converging magnetic field lines reflect charged particles back toward regions of weaker magnetic field. Sin²(θ_loss) = B_min / B_max (Loss Cone Angle)

Magnetic Permeability Electromagnetism & Electronics H/m (or T·m/A) A material property measuring the degree to which a medium supports and concentrates magnetic flux inside itself when subjected to a magnetic field. μ = B / H = μ_r μ₀, μ₀ = 4π × 10⁻⁷ T·m/A

Magnetic Reconnection Plasma Physics MW or Joules (Energy Conversion) A fundamental plasma process where opposing magnetic field lines break and explosively reconnect, releasing stored magnetic field energy into kinetic and thermal particle energy. E_reconnection ≈ M_A v_A B (Alfvénic Reconnection Rate)

Magnetic Resonance Imaging (MRI) Biophysics & Medical Physics Tesla B₀ (~1.5–3.0 T) & MHz A non-invasive medical imaging modality utilizing powerful magnetic fields, radiofrequency (RF) pulses, and nuclear magnetic resonance (NMR) of hydrogen protons to image soft tissue. Larmor Frequency ν₀ = (γ / 2π) B₀ (γ_proton ≈ 42.58 MHz/T)

Magnetic Susceptibility Electromagnetism & Electronics Dimensionless A dimensionless material property measuring the degree of magnetization induced in a material per unit applied magnetic field strength. M = χ_m H, μ_r = 1 + χ_m

Magnetized Target Fusion (MTF) Plasma Physics Hybrid Density & Time Scale A hybrid fusion approach that combines magnetic confinement thermal insulation with rapid mechanical or laser inertial compression. Hybrid MTF: Density n ~ 10²⁴ m⁻³, Confinement Time τ_E ~ 1 μs–1 ms

Magnetoencephalography (MEG) Biophysics & Medical Physics fT (Femtoteslas = 10⁻¹⁵ T) A non-invasive functional neuroimaging technique mapping brain activity by measuring weak magnetic fields produced by neuronal electric currents using SQUID sensors. Magnetic Field B ~ 10–100 fT (10⁻¹⁵ Tesla)

Magnetohydrodynamics Plasma Physics MHD Equations Framework The fluid framework describing the macroscopic dynamics and magnetic field interactions of electrically conducting fluids and magnetized plasmas. ∂B / ∂t = ∇ × (v × B) + η ∇²B, ρ (dv/dt) = -∇p + J × B + ρ g

Magnetosphere Geophysics & Environmental Physics Earth Radii (R_E ~ 10 R_E sunward) The region of space surrounding Earth dominated by Earth's geomagnetic field, shielding the planet from harmful solar wind plasma. Magnetopause Distance R_mp ≈ (B₀² / (2 μ₀ ρ v²))^(1/6)

Magnetron Sputtering Plasma Physics nm/s (Deposition Rate) A physical vapor deposition (PVD) technique utilizing magnetically confined glow discharge plasma to sputter target material onto substrates. E × B Electron Trapping drift path near cathode target

Magnification Optics Dimensionless The ratio of image height to object height, or ratio of image distance to object distance in an optical system. m = h_image / h_object = -v / u

Main Sequence Astrophysics, Cosmology & Relativity H-R Diagram Band The continuous evolutionary diagonal band on the Hertzsprung-Russell diagram containing stars fusing hydrogen into helium in their cores. L ∝ M^3.5 (Mass-Luminosity Relation)

Majority & Minority Carriers Condensed Matter & Materials Physics cm⁻³ (Carrier Density) The classification of charge carriers in a doped semiconductor based on their relative concentrations. N-Type: n_majority = N_D, p_minority = n_i² / N_D

Malleability Condensed Matter & Materials Physics Qualitative / Quantitative Plastic Strain A material's physical ability to deform plastically under compressive stress without cracking, typically tested by hammering or rolling into thin sheets. Compressive strain tolerance without cracking

Malus's Law Optics W/m² The law stating that intensity of linearly polarized light transmitted through an analyzer is proportional to the squared cosine of the angle between polarizer and analyzer transmission axes. I = I0 cos² θ

Mantle Convection Geophysics & Environmental Physics cm/year (Convection Motion Speed) The slow, highly viscous thermal convection currents within Earth's solid silicate mantle transporting internal core heat toward the surface. Ra = (ρ g α ΔT d³) / (κ η) (Rayleigh Number > Ra_critical)

Martensitic Transformation Condensed Matter & Materials Physics Transformation Temperature M_s A rapid, diffusionless solid-state phase transformation driven by collective lattice shear displacement of atoms. Diffusionless shear transformation: Austenite (FCC) → Martensite (BCT)

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