Glossary of Physics (M)

 
Magnetic domain: Small regions in permanent magnets within which atomic or molecular magnetic moments are aligned parallel.
Magnetic field: The region around a magnet where its magnetic force is experienced by other magnetic objects.
Magnetic reversal: The changing of polarity of the earth's magnetic field as the north magnetic pole and the south magnetic pole exchange positions.
Magnetic wave: The spread of magnetization from a small portion of a substance where an abrupt change in the magnetic field has taken place.
Magnification: The ratio of the size of the image to the size of the object.
Malus law: The intensity of the light transmitted from the analyzer varies directly as the square of the cosine of the angle between the plane of transmission of analyzer and polarizer.
Maser: Microwave amplification by stimulated emission of radiation.
Mass defect: The difference between the sum of the masses of the individual nucleons forming a nucleus and the actual mass of that nucleus.
Mass number: The sum of the number of protons and neutrons in a nucleus.
Mean life: The average time during which a system, such as an atom, nucleus, exists in a specified form.
Mechanical energy: The sum of energy possessed by a body due to its position, configuration and motion.
Mechanical wave: The waves, which need a material medium for their propagation, e.g., Sound waves.
MeV: Unit of energy, equal to 1.6 x 10-13 joules.
Megahertz: Unit of frequency, equal to 106 hertz.
Millibar: A measure of atmospheric pressure equivalent to 1000 dynes per cm 2.
Modulus of elasticity: The ratio of stress to the strain produced in a body.
Modulus of rigidity: The ratio of tangential stress to the shear strain produced in a body.
Mole: The amount of a substance that contains Avogadro's number of atoms, ions, molecules, or any other chemical unit; a mole is 6.02 x 1023 atoms, ions, or other chemical units.
Momentum: The product of mass and velocity of a body, it is a measure of the quantity of motion in a body.
Monochromatic light: Consisting of single wavelength.