Magnetic dipoles – a north and south pole separated by a fixed distance

Magnetic dipole moment – the product of the magnetic pole strength and the distance between the north and south of the magnetic dipole

Magnetic domains – small regions in solids in which the ionic moments are similarly aligned

Magnetic field – the area over which a magnetic force exists, designated by magnetic field lines (see field lines)

Magnetic flux – the product of the magnitude of the magnetic field, the magnitude of surface area, and the cosine of the angel between the direction of the field and the normal to the surface (see equation 19.2)

Magnetic quantum number – the magnitude of the component of the angular momentum along a particular spatial direction

Magnifying glass – a single converging lens that, when held near the eye, gives an image whose size on the retina is larger than that observed by the unaided eye

Magnitude of a vector - the scalar number which gives the length of a vector

Malus's law – the relative intensity of light that passes through two polarizers is proportional to the square of the cosine of the angle between their planes of polarization (see equation 24.11)

Mass – the quantitative measure of the inertia of a body

Mass-energy relation – a generalization of the law of conservation of energy that includes mass, represented by the famous equation E=mc² (see equation 25.6)

Maxwell-Boltzmann distribution – gives the fraction of particles of a gas within a range of speeds ( see equation 12.12)

Maxwell’s electromagnetic equations – four equations (Gauss's law, Gauss's law for magnetism, Faraday's law and Ampere's law, with an addition by Maxwell) used to interpret and explain an array of electromagnetic phenomena (see section 20.8)

Mechanical energy – the sum of a body’s kinetic energy and potential energy

Mechanics – the branch of physics that deals with the kinetics and dynamics of macroscopic (large-scale) objects

Mesons – a group of particles whose first members have masses between the masses of the electron and the proton, while more newly discovered ones are more massive

Metastable state – an excited electronic energy state that has a relatively long lifetime

Mobility – the magnitude of the drift velocity per unit field (see equation 31.6)

Model – an idealized description of a physical system or natural phenomenon

Mole – the amount of a material which contains Avogadro's number of molecules and whose mass in grams is numerically equal to the molecular mass of the substance

Moment of inertia – the mass of a rotating object times the square of the distance to the axis of rotation

Momentum - the product of mass (m) times velocity (v)

Moseley’s law – gives a relationship between the wavelength of an x ray line and the nuclear charge (see equation 27.13)

Muon – a charged (positive or negative) particle associated with the nuclear force field with a weak interaction with matter and a spin similar to the electron