Magnon
Quantum
of a spin wave.
(or)
A quasi particle introduced to describe small
departures from complete ordering of electron spins in ferro, ferri, and antiferro-
magnetic substances.
Majarona
Forces
A nuclear force
in which there is exchange of position coordinates only but not spin
coordinates.
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.
Marginal
Rays
The rays of light
incident from the principle axis are called marginal rays.
Mars
It is fourth
planet from sun in our solar system named after Roman god of war; which has
period of revolution about sun of 687 days at a mean distance of 227.9 million
km and a mean diameter of approximately 6,794kms.
Martensite
It is a meta-stable
iron phase super saturated in Carbon that is the product of diffusion less
transformation from Austenitic.
MASER
It is acronym for
Microwave Amplification by Stimulated Emission of radiation. First MASER was
built in 1951 by Charles. H. Townes. It is a device for coherent amplification
or generation of electromagnetic waves by use of excitation energy in resonant
atomic or molecular systems. The device uses an unstable ensemble of atoms or
molecules that may be stimulated by an electromagnetic wave to radiate energy
at same frequency and phase as simulating wave, thus providing coherent
amplification.
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.
Mass
Number
It is the number which represents the total
sum of nucleons for a particular atom. It is denoted as superscript to an
element.
Mass
Spectrometer
Mass spectroscopy
is a methodology that is extensively used to determine properties of charged
particles. The basic principle of this technique is to dissociate the sample
into smaller fragments and then let them pass through a high magnetic field.
The charged particles get deflected in the magnetic field with the degree of
deflection proportional to their mass to charge ratio (m/e). These deflected
particles are then collected by a position sensitive detector, such as a micro channel
PMT.
Mass
Mass is an
attribute and not a physical thing. Mass is the attribute “inertia” of a
physical object or of whatever is contained in a specific region of space.
Materialistic
Wave
Louis de Broglie postulated that a wave has to be
associated with each moving material particle called as matter wave. The
wavelength of this wave is determined by momentum of particle. The waves are
not perceptible for macroscopic bodies but for microscopic bodies.
Material
Science/Engineering
The discipline of materials science
involves the investigating the relationships that exist between the structures
and properties of materials. In contrast, Materials Engineering is on the basis
of these structure-property correlations, designing or engineering the
structure of a material to produce a predetermined set of properties.
Matheissan’s
Rule
According to this
rule, electrical resistivity of metals is sum of resistivity due to impurities
and temperature dependant resistivity. Even
at absolute zero, the metals have non zero resistivity which is due to presence
of impurities.
Matter
It is tangible stuff; what when one can touch and sense with your hands
and so a physical thing.
Maxwell
The CGS unit of magnetic flux defined as the flux through one
square centimeter normal to a magnetic field of 1 Gauss.
Mcleod
Gauge
A McLeod gauge is
an absolute pressure standard to which many other vacuum gauges are
calibrated. It will accurately measure the total pressure of
non-condensable permanent gases (i.e. hydrogen, nitrogen, oxygen, etc.) in a
vacuum system, but will not correctly measure condensable vapors if present. This
form of vacuum gauge was invented in 1874 By H. G. McLeod to measure pressures
of the order of 10-2 to 10-7 Torr. The calibration of the
gauge for non-condensable gases is based upon Boyles’ law for gases and
therefore measurement of the volume of the glass bulb and the volume per unit
length or bore of the capillary tubes is made with high precision.
Mean
The mean, except
in statistics courses and scientific journals, is more commonly known as the average.
The mean is perhaps the most widely used and reported measure of central
tendency. The mean is quite simple to calculate: Simply add all the numbers in
the data set and then divide by the total number of entries. The result is the
mean of the distribution.
Mean
Free Path
It is a
microscopic quantity of a matter which is defined as average distance travelled
by an atom/molecule/electron between two successive collisions in a medium.
Mean
Deviation
The average of
the deviations of the individual values from the arithmetic mean is called mean
deviation.
Mean
Life (Radiation Physics)
Reciprocal
of decay constant is called average life of radioactive species.
Mechanical
Energy
It is energy possessed by an object by
virtue of its kinetic energy or potential energy or combination of both.
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
