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Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic Letter 1_ V


vacuum
video m

vacuum. Space from which air has been removed and thus contains only a few particles of matter. A cubic meter of air at normal pressure contains about 1025 particles. The number for a good vacuum on Earth is about 1014.
The value between the Earth and the Moon is much lower, but between the galaxies there may be a real void.
However, the vacuum of outer space contains energy in forms other than matter, such as force fields, radiation, and extremely low-mass particles called neutrinos.


vacuum flask
vase m dewar

Vacuum flask. The design of this bottle is intended to
Reducing the energy transmission between the contents and the outside greatly. The four ways of energy transfer are as follows:

- “Conduction”: through the vacuum, the insulating box, and the plug.

- “Convection”: by means of vacuum, foam, and plug.

- Radiation: from the glass surface
The preferred one.

- Evaporation: using the plug and the lid. Despite all these barriers, some energy transfer must occur.
Also called Dewar flask.

valve
valve f

Valve. A general expression for a one-way door. The mechanical valve in the car tire allows air to enter but not to exit. An electric valve allows electricity to flow in only one direction. The first electric valves allowed electrons to flow from a hot anode to a cold cathode through a vacuum, and were called diodes.

There are a number of other types of electronic valves in use, some have more than three paths and some are gas-filled.

Semiconductor devices have replaced electronic valves in many types of circuits.
Also called electron tube.


Van der Graaff machine
motor m Van der Graaff

Thanh de graff machine. A machine that can generate very high voltages by electrostatic means.
During use, the cue ball gains more and more charge until the electric field around it causes the air to disintegrate. Then a spark discharge may occur, or there may be a constant moderate leak. The maximum voltage values ​​usually reach 500 kV. The very large models used in research can give voltages up to 100 megavolts. Small machines do not need a high-tension feed because friction provides the primary charge.


vapour
vapor f

Vapor is a substance in a gaseous state that can be converted into a liquid by pressure. This cannot be done at a temperature higher than the critical temperature Tc of the material. Any liquid or solid can evaporate to a certain extent at any temperature. The saturation vapor pressure of a substance is the pressure exerted by the vapor in equilibrium with the liquid. The figure below shows how the saturation vapor pressure changes with temperature.

This drawing is very useful because the curve itself appears out of context. As shown, it relates the saturation vapor pressure p of the sample to its temperature T. It can also show:

* How does the boiling temperature T depend on the external pressure p? See pressure cooker.

* The pressure p required to liquefy the steam at a temperature of T.

* Whether the substance is a liquid, vapor, or gas at a given pressure/temperature (see state change).


vector
vector m

Vector. Measurement includes both size and direction. (Scalar only measures size.) Examples include: speed, momentum, and force field strength.