## Pages

### PHYSICS DICTIONARY

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Mean free path
Average distance traveled by an atom/molecule/electron between two successive collisions in a medium.

Moderation
It is referred as method of slowing down of neutrons in the range from fission energies to roughly below 1eV.

Miller Indices
A set of 3 integers (four for hexagonal structure) that designate crystallographic planes, as determined from reciprocal of fractional axial intercepts.

Magnetic susceptibility
The proportionality constant between magnetization and magnetic field strength is called as magnetic susceptibility.

Mechanical Equilibrium
When there is no unbalanced force between system and its surroundings, the system is said to be in mechanical equilibrium.

Mechanical Equivalent of heat
It is defined as work done to produce a quantity of heat. It is denoted by ‘J’. J=W/H. In CGS system ‘W’ is ergs ‘H’ in calories, J= 4.18 Joules/Cal

Microscope
It is device using converging lens of short focal length. When an object is seen through this device, an erect, magnified and virtual image of object is seen.

Moment of Inertia
It is the inertia of rotation of a body about the given axis.

Micro canonical ensemble
It is the collection of a large number of essentially independent systems having the same energy ‘E’, volume ‘V’ and number of particles ‘N’. The individual systems of a micro canonical ensemble are separated by rigid, impermeable and well insulated walls such that values of E,V, N for a particular system are not affected by presence of other systems.

Mutual Induction
When two coils are placed near each other such that the current flowing in one changes emf is induced in second coil, such phenomenon is known as mutual induction.

Milliman’s Theorem
It states that if several voltages sources are in series with admittances are connected then equivalent circuit is represented by voltage source in series with impedance.

Mass defect
The measured mass or actual mass of atom is less than sum of masses of constituent nucleons. The difference is referred to as mass defect.

Molecular spectrum
Spectrum which arises from rotation of a molecule as a whole and vibrations of its constituent atoms relative to one another as well as changes in its electronic configuration.

Mirror Nuclei
Nuclei having same mass number but with proton & Neutron number interchanged.

Meissner effect
The property of exhibiting perfect diamagnetism by super conductor is called Meissner effect.

Mass number
It is sum of total number of protons and neutrons inside nucleus of an atom.

Molecular range
The maximum distance up to which a molecule exerts force of attraction is called as molecular range.

Mobility
Drift velocity of charge carriers per unit electric field

Molar specific heat
Amount of heat required raise the temperature by one degree centigrade of one Kelvin.

Moseley’s Law for X-rays
The frequency of a spectral line in characteristic X-ray spectrum varies directly as square of atomic number Z of element emitting it.

Manometer
Device used to measure pressure in terms of difference in height of two mercury columns, one open to atmosphere and other connected to source of unknown pressure.

Mean free path
Average distance travelled by a molecule in a gas between two successive collisions with other molecules of the gas.

Modulus of resilience
The strain energy per unit volume required stress a material from an unloaded state up to the point of yield.

Molecular weight
It is the sum of atomic weights of all atoms in a molecule.

Magnetization
The total magnetic moment per unit volume of material is called as magnetization.

Martensite
It is a meta stable iron phase super saturated in Carbon that is the product of a diffusion less transformation from Austenitic.

Mole
It is the quantity of a substance, which corresponds to Avogadro’s number i.e. 6.023 x 1023 atoms.