Vacancy
Diffusion
The diffusion
mechanism where in net atomic migration is from lattice site to an adjacent
vacancy.
Vacancy
A normally occupied lattice site in crystal
from which an atom or ion is missing.
Vacuum
Pressure
If pressure of a
fluid is below atmospheric pressure, it is designated as gauge pressure.
Vacuum
According to
definition of American vacuum society, “vacuum” refers to a given space filled
with gas at pressures below atmospheric i.e. having a density of molecules less
than about 2.5 x 1019 molecules /cm3.
Valence
Band
For solids, the electron energy levels band
that contains valence electrons. These electrons lie in outermost orbits of
atoms at absolute zero temperature.
Valence
Electrons
The electrons occupying outermost orbits
which usually participate in interatomic bonding are called as valence
electrons.
Van
De Graff Generator
It was invented by American physicist Robert J.
VandeGraff in 1929. It is a machine capable of building up potential difference
of few million volts, and fields close to breakdown field of air which is about
3x106 V/m. The potential is build up with help of static change by
friction.
Vanderwaal’s
Gas
See real gas
Vanderwalls
Bond
A secondary
interatomic bond between adjacent molecular dipoles, which may be permanent or
induced is called Vanderwall’s bond. They are formed as a result of dipole
attractions, the dipoles being formed as a result of unbalanced distribution of
electrons in asymmetrical molecules.
Vapor
Gaseous state below the critical
temperature of substance is known as vapor.
Vapor
Degreasing
The process in
which solvent is heated to boiling point, and parts to be cleaned are hung in
the chamber exposing to hot vapors. The vapors get condensed on metal surfaces
during which dissolves oil & grease and flows back to solvent condition.
Variance
The variance
gives us a sense of how closely concentrated a set of values is around its
average value, and is calculated in the following manner: Subtract the mean of
the distribution from each of the values. Square each result. Add all of the
squared results. Divide the result by the number of values minus 1.
Vector
Product
See cross product.
Vector
It is a physical quantity having both
magnitude and direction and which obey laws of vector addition.
Velocity
Addition Theorem
The addition of
any velocity to the velocity of light merely reproduces again the velocity of
light. Thus velocity of light is maximum range of velocity attainable in
nature.
Velocity
Gradient
It is rate of change of velocity of liquid
layers with distance, the distance being taken normal to the direction of flow.
Vibration
It is the to & fro motion of a particle
from one extreme position to the other and back again. It is motion of a
particle from mean position to one extreme position, then to other extreme
position and finally back to mean position.
Vibration-Rotational
Spectrum
Molecular spectra obtained in near infrared
region.
Virtual
Image
A
virtual mage is formed at a position where the paths of principal rays cross
when projected backward from their paths beyond the lens. Although a virtual
image does not form a visible projection a screen, it is no sense “imaginary”
i.e. it has a definite position and size and can be “seen” or imaged by the
eye, camera or other optical instrument.
or
When
a beam of light diverging from a point after reflection (or refraction) appears
to diverge from second point, then the second point is called as virtual image
of first. The virtual image cannot be formed on screen.
