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Virtual image:

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.

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. 

VVER:

Acronym for Voda Vodyanoi Energitechesky reactor (water cooled water moderated energy reactor)

Vapour degreasing:  

The process in which solvent is heated to boiling point and parts to be cleaned are hung in the chamber exposing to hot vapours. The vapours get condensed on metal surfaces during which dissolves oil & grease and flows back to solvent condition.

Vacuum pressure:

If pressure of a fluid is below atmospheric pressure it is designated as gauge pressure.

Vitrification:

During firing of a ceramic body, the formation of a liquid phase that upon cooling becomes a glass bonding matrix.

Vapor:

Gaseous state below the critical temperature of substance is known as vapor.

Vector:

It is a physical quantity having both magnitude and direction and which obey laws of vector addition.

Volume strain:

It is the change in volume per unit original volume or it is the fractional change in volume.

Viscosity:

It is the property of a fluid which opposes the relative motion between its layers. Viscosity is known as fluid friction.

Vacuum pressure:

If pressure of a fluid is below atmospheric pressure it is designated as vacuum pressure.

Vibrational-rotational spectrum:

Molecular spectra obtained in near infrared region.

Visible spectrum:

Molecular spectrum obtained in visible or ultra violet region.