A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Diamagnetism
It is a very weak form of magnetism that is
non permanent and persists only while an external field is being applied. It is
induced by a change in orbital motion of electrons due to an applied magnetic
field. The magnitude of induced magnetic moment is extremely small, and in a
direction opposite to that of applied field. Thus relative permeability is less
than unity and magnetic susceptibility is negative. When placed between poles
of strong electromagnet, diamagnetic materials are attracted towards regions
where field is weak.
Diamond
A pure extremely
hard, high refractive crystalline form of carbon naturally crystallized in
isometric system, which is usually colorless and is used as a gemstone and in
abrasives, cutting tools etc.
Diatomic
Molecule
Molecule
containing two atoms.
Diatonic
Scale
It is a musical
scale in which 8 tones of some definite frequencies are arranged such that the
frequency of the 8th tone is twice the frequency of 1st
tone.
Dielectric
Constant
It is macroscopic
quantity that measures how effectively an electric field polarizes the
material. It is property of a dielectric material which determines the amount
of electrostatic energy that can be stored by material when a given voltage is
applied to it.
Dielectric
Materials
They are materials
which are electrical insulators or in which an electric field can be sustained
with a minimal dissipation of power. There are two types of dielectrics: i)
Polar ii) Non-polar. The dielectrics are used for separation of conductors in
capacitors to store energy.
Dielectric
Strength
The maximum
electric field, a dielectric can withstand before reaching breakdown condition
is called as dielectric strength of dielectric.
Differential
Equation
A differential equation
is the mathematical equation for an unknown function of one or several
variables that relates the values of the function itself and its derivatives of
various orders.
Differentiation
Derivative of
continuous function at a given value will give rate of change of function near
that value.
Diffraction
The
bending of waves at the corners of an object is called diffraction.
(or)
Deviation
of light from rectilinear path is called as diffraction. The phenomenon was
discovered by Grimald in 1665.
Diffusion
Coefficient
It is the
constant of proportionality between the diffusion flux and the concentration
gradient in the Fick’s first law. Its magnitude is indicative of rate of atomic
diffusion.
Diffusion
Flux
The quantity of
mass diffusing through and perpendicular to a unit crossectional area of
material per unit time is called as diffusion flux.
Diffusion
Pump
Pump used to
attain high vacuum of order 10-6 mbar. The pump consists of leak tight enclosure in
which there is bath of fluid having low boiling point, surrounded by heating
coil. Water is circulated on the side walls of container to prevent thermal run
away. The fluid which gets heated turns to vapor and rises above. Upon cooling,
the fluid falls again to bath with high speed. While falling, the fluid takes
the air molecules and thus creates low pressure region at the top. Due to this
low pressure region, there is transport of molecules from the system to be
evacuated. The molecules diffuse into vapor jet in a diffusion manner.
Diffusion
Physical
phenomenon of transport of mass by atomic motion due to difference in
concentration levels is called as diffusion.
Diffusivity
(Mass ) or Diffusion Coefficient
The rate, at
which quantity of a substance diffuses from one region to another region
through each unit of crossection per unit time when the volume concentration
gradient is unity, is called as diffusivity.
Diffusivity
(Thermal)
It is measure of
ability of a substance to transmit heat for a difference in temperature. It is
expressed as thermal conductivity divided by the product of specific heat
capacity and density. It is measure of thermal inertia.
Digit
Symbol used to
make numerical.
Digital
Technology of
representing data using discrete values.
Dilatometer
Scientific
instrument that measures volume changes caused by a physical or chemical
process.
Dilute Magnetic Semiconductor
Alloy formed by replacing few original atoms in semiconductor by magnetic elements. The most common dilute magnetic semiconductors are II-VI compounds (like CdTe, ZnSe, CdSe, CdS, etc.), with transition metal ions (e.g. Mn, Fe or Co) substituting their original cations. The information is not only carried by charge but also spin of electrons, an additional degree of freedom. The compounds are useful for novel electronic devices.
