Dictionary of Physics by Frantisek Fecko: V

vacancy	vakancia	Point defect created by missing atom or ion.
vacuum	vákuum	A space in which there is a low pressure of gas, i.e. relatively few atoms or molecules. A perfect vacuum would contain no atoms or molecules.
vacuum state	vákuový stav	The ground state in a relativistic quantum field theory. It has a zero-point energy, which gives rise to vacuum fluctuations.
valence band	valenčné pásmo	In the band theory of solids, the energy band occupied by the valence electrons.
valence electron	valenčný elektrón	An electron in one of the outer shells of an atom that takes part in forming chemical bonds.
valence shell	valenčná vrstva, valenčná sféra	The outer electron shell of an atom, containing the valence electrons.
valency	valencia, mocenstvo	The combining power of an atom or radical, equal to the number of hydrogen atoms that the atom could combine with or displace in a chemical compound (hydrogen has a valency of 1).
valve	1. ventil 2. elektrónka	1. Any device that can be closed or open to allow a fluid to pass through it. 2. Short for thermionic valve.
Van Allen belts	Van Allenove pásy	Belts that are sources of intense radiation surrounding the earth, consisting of high-energy charged particles trapped in the earth’s magnetic field within which they follow roughly helical paths.
Van de Graaff generator	Van de Graafov generátor	An electrostatic generator used to produce high voltage.
Van der Waals’ bond	Van der Waalsova väzba	A very weak bond that holds separate molecules together in molecular solids such as solid carbon dioxide. The bond originates from the Van der Waals’ force between neutral molecules.
Van der Waals’ force	Van der Waalsova sila	An attractive force between atoms or molecules.
vapour	para, výpar(y)	The gaseous state of a substance below its boiling point.
variable resistor	rezistor s meniteľným odporom	A resistor whose resistance can be changed, made from a layer of resistance material with a sliding contact. Depending on the way it is connected in a circuit, variable resistor can function as potentiometer or rheostat.
vector	vektor	A quantity in which both the magnitude and the direction must be stated. Examples of vector quantities: acceleration (a), velocity (v), force (F) etc. Compare scalar.
vector product	vektorový súčin	The product of two vectors u and v, with components u₁, u₂, u₃ and v₁, v₂, v₃ respectively, given by u x v = (u₂v₃ - u₃v₂)i + (u₃v₁ - u₁v₃)j + (u₁v₂ - u₂v₁)k. It is itself a vector, perpendicular to both u and v.
velocity	rýchlosť	Symbol v. The rate of displacement of a body. It is the speed of a body in a specified direction and is measured in m.s^-1.
very high frequency (VHF)	veľmi vysoké vlny	A radio frequency in the range 300 MHz - 30 MHz.
very low frequency (VLF)	veľmi nízke vlny	A radio frequency in the range 30 kHz - 3 kHz.
VHF band	pásmo VKV, pásmo VHF	The range (band) of radio frequency between 300 MHz and 30 MHz.
virtual image	neskutočný obraz	An image seen at a point from which the rays appear to come to the observer, but do not actually do so.
virtual particle	virtuálna častica	In quantum theory, a particle whose permanent existence is forbidden by the law of conservation of energy, but which can exist temporarily according to Heisenberg’s uncertainty principle.
virtual state	virtuálny stav	The state of the virtual particles that are exchanged between two interacting charged particles.
viscosity	viskozita	A measure of the resistance to flow in a fluid.
visible spectrum	viditeľné spektrum	The spectrum of electromagnetic radiation to which the human eye is sensitive, approximately from 3.8 x 10¹⁴ Hz (780 nm, red) to 7.8 x 10¹⁴ Hz (380 nm, violet).
visual binary	viditeľná dvojhviezda	Binary star in which the stars are far enough apart to be seen separately by an optical telescope.
vitreous humour	sklovec	Part of a human eye.
volt	volt	Symbol V. The SI unit of electric potential, potential difference, or e.m.f..
voltage	napätie	Symbol V (also U). An e.m.f. or potential difference expressed in volts.
voltage divider	delič napätia	Two resistors connected in series so that they divide the total voltage U into voltages U₁ and U₂. U₂ = U.R₂/(R₁ + R₂)
voltaic cell	galvanický článok	A device that produces an e.m.f. as a result of chemical reactions that take place within it.
voltmeter	voltmeter	An instrument used to measure voltage, i.e. potential difference in volts.
volume	objem	Symbol V. The space occupied by a body or mass of fluid. It is measured in m³.
W boson	W-bozón	The charged particle that, together with the neutral Z boson, are the gauge bosons responsible for the weak nuclear force. There are two oppositely charged W particles, W⁺ and W^-.
watt	watt	Symbol W. The SI unit of power.
wattmeter	wattmeter	An instrument for measuring the power in watts in an alternating-current electric circuit.
wave	vlna, vlnenie	A periodic disturbance in a medium or in space.
wave equation	vlnová rovnica	²u = (1/v²)δ²u/δt², where ² = δ²/δx² + δ²/δy² + δ²/δz² is the Laplace operator, u is the displacement, and v is the speed of propagation.
wave form	tvar vlny	The shape of a wave or the pattern representing a vibration.
wave function	vlnová funkcia	A function y(x,y,z) appearing in Schrödinger’s equation in quantum mechanics. The wave function is a mathematical expression involving the coordinates of a particle in space. The physical significance of the wave function is that the square of its absolute value, \|y\|², at a point is proportional to the probability of finding the particle in a small element of volume, dxdydz, at that point.
wave number	vlnové číslo	Symbol k. The number of cycles of a wave in unit length. If the wavelength of the wave is l, then k = 1/l.
wave theory	vlnová teória svetla	The theory of light in which it was regarded as a wave, thus successfully explaining the interference of light. The theory led to showing that light forms part of the electromagnetic spectrum (James Clark Maxwell).
wavefront	čelo vlny	A line or surface within a two- or three-dimensional medium through which waves are passing, being the locus of all adjacent points at which the disturbances are in phase.
wavelength	vlnová dĺžka	Symbol l. The closest distance between two points in a wave that are moving in phase, for example the distance between two adjacent peaks. It is measured in metres.
wave-particle duality	vlnovo-časticový dualizmus	The concept that waves carrying energy may have a corpuscular aspect and that particles may have a wave aspect.
weak interaction	slabá interakcia	One of the four fundamental interactions, some 10¹⁰ times weaker than the electromagnetic interaction, that occurs between leptons and in the decay of hadrons. It is responsible for beta decay of particles and nuclei.
weakly interactive massive particle (wimp)	slabo-interagujúca ťažká častica	In cosmology, one hypothetical form of missing mass in the universe.
weber	weber	Symbol Wb. The SI unit of magnetic flux.
wedge	klínový mechanizmus	One of the six simple machines.
weight	tiaž	The force by which a body is attracted to the earth.
weightlessness	beztiažový stav	The apparent absence of gravity experienced in an orbiting spacecraft, or any other object falling freely in a gravitational field.
Wheatstone bridge	Wheatstoneov mostík	An electrical circuit for measuring the value of a resistance, consisting of three resistors of known values and one resistor of unknown value which we want to find out, and a galvanometer.
white dwarf	biely trpaslík	A very small hot star. As the surface area is small the luminosity is low. Such stars lie at the bottom left of the Hertzsprung-Russel diagram.
Wien’s displacement law	Wienov posunovací zákon	For a black body, l_maxT = constant, where l_max is the wavelength corresponding to the maximum radiation of energy and T is the thermodynamic temperature of the body.
WIMP	wimp	Weakly interacting massive particle.
work	práca	Symbol W. The work done by a force acting on a body is the product of the force (F) and the distance (s) moved by its point of application in the direction of the force. W = F.s.cos j, where j is the angle between the direction of the displacement and direction of the force. It is measured in joules (J).
work function	výstupná práca	Short for work function energy.
work function energy	výstupná práca	Symbol W_v. The minimum amount of energy needed to remove an electron from the surface of a metal in the photoelectric effect. W_v = hf - E_k = hf₀, where h is the Planck constant, f the frequency of the electromagnetic radiation, E_k is the kinetic energy of the photoelectron, and f₀ is the threshold frequency.
X-ray sources	zdroje Roentgenoveho žiarenia	Sources of X-radiation from outside the solar system.
X-ray tube	Roentgenova trubica	A device for generating X-rays by accelerating electrons to a high energy by an electrostatic field and making them strike a metal target either in a tube containing a low-pressure gas, or in a high vacuum.
X-rays	Roentgenove lúče	Electromagnetic radiation of shorter wavelength than ultraviolet radiation produced by bombardment of atoms by high-quantum-energy particles. The range of wavelengths is 10^-11 m to 10^-9 m.
Yagi aerial	anténa Yagi	A directional aerial array widely used for television and radio telescopes.
Yang-Mills theory	Yang-Millsova teória	Another name for a non-Abelian gauge theory.
yard	jard	Symbol yd. The former Imperial standard unit of length. 1 yd = 3 ft = 0.9144 m
year	rok	The measure of time on which the calendar is based. It is the time taken for the Earth to complete one orbit of the Sun. See also Calendar year; Solar year; Sidereal year; Anomalistic year.
yield point	medza klzu	See elasticity.
Young modulus of elasticity	Youngov modul pružnosti	Symbol E. The ratio of the longitudinal stress (s_n) applied to a body to the longitudinal strain (e) produced. E = s_n/e
Young’s slits	Youngove štrbiny	The apparatus for proving the interference of light.
Z boson	Z-bozón	An electrically neutral elementary particle, Z⁰, that together with charged W boson are the gauge bosons responsible for the weak nuclear force.
Zeeman effect	Zeemanov jav	The splitting of the lines in a spectrum when the source of the spectrum is exposed to a magnetic field. See also normal Zeeman effect and anomalous Zeeman effect.
Zener diode	Zenerova dióda	A type of semiconductor diode, consisting of a p-n junction with high doping concentrations on either side of the junction
zenith	zenit	The point on the celestial sphere that lies directly above an observer. Compare nadir.
zero vector	nulový vektor	A vector with magnitude equal to 0.
zero-point energy	energia nulového bodu	The energy remaining in a substance at the absolute zero of temperature (0 K).
zeroth law of thermodynamics	nultý termodynamický zákon	A definition of the concept of temperature, which states that if two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other.
zinc-carbon cell (dry cell)	zinok-uhlíkový článok (suchý článok)	A common type of electrolytic cell, which gives an e.m.f. of about 1.5 V and is not rechargeable.
zodiac	zverokruh, zodiak	A band that passes round the celestial sphere, extending 9º on either side of the ecliptic. It includes the apparent paths of the Sun, Moon, and planets (except Pluto). The band is divided into the twelve signs of the zodiac, each 30º wide.