Dictionary of Physics by Frantisek Fecko: D

D to A converter	D/A prevodník	Same as digital-to-analogue converter.
dalton	dalton	Another name for atomic mass unit.
Dalton’s law	Daltonov zákon	The total pressure of a mixture of gases or vapours is equal to the sum of the partial pressures of its components.
damping	tlmenie (kmitania)	A decrease in the amplitude of an oscillation as a result of energy being drained from the oscillating system to overcome frictional or other resistive forces.
dark matter	tmavá hmota	See missing mass.
dating techniques	techniky datovania, techniky určenia veku	Methods of estimating the true age of rocks, palaeontological specimens, archaeological sites, etc.
daughter	dcérsky nuklid, dcéra	A nuclide produced by radioactive decay of some other nuclide (the parent).
day	deň	The time taken for the earth to complete one revolution on its axis.
de Broglie wavelength	de Broglieho vlnová dĺžka	The wavelength (l) of the wave associated with a moving particle. l = h/(mv) where h is the Planck constant, m is the mass of the particle, and v its velocity.
decay	rozpad	The spontaneous transformation of one radioactive nuclide into a daughter nuclide, which may be radioactive or may not, with the emission of one or more particles or photons.
decibel	decibel	Symbol dB. A unit used to compare two power levels, usually applied to sound or electrical signals.
declination	deklinácia	The angular distance of a celestial body north (positive) or south (negative) of the celestial equator.
deconfinment temperature	odväzňovacia teplota	The temperature at which quarks may become free.
defect	porucha [kryštálovej mriežky]	A discontinuity in a crystal lattice.
degeneracy pressure	degeneračný tlak	The pressure in a degenerate gas of fermions caused by the Pauli exclusion principle and the Heisenberg uncertainty principle.
degenerate gas	degenerovaný plyn	A gas in which, because of high density, the particle concentration is so high that the Maxwell-Boltzmann distribution does not apply and the behaviour of the gas is governed by quantum statistics.
degenerate level	degeneračná hladina	An energy level of a quantum-mechanical system that corresponds to more than one quantum state.
degenerate semiconductor	degenerovaný polovodič	A heavily doped semiconductor in which the fermi level is located in either the valence band or the conduction band.
degenerate states	degenerované stavy	Quantum states of a system that have the same energy.
degree	stupeň	1. A unit of plane angle equal to 1/360th of a complete revolution. 2. A division on a temperature scale.
degrees of freedom	stupne voľnosti	The number of independent parameters required to specify the configuration of a system.
delay line	oneskorovacia linka	A component in an electrical circuit that is introduced to provide a specific delay in transmitting the signal.
delayed neutrons	oneskorené neutróny	The small proportions of neutrons that are emitted with a measurable time delay in a nuclear fission process. Compare prompt neutrons.
demagnetisation	demagnetizácia	The removal of the ferromagnetic properties of a body by disordering the domain structure.
demodulation	demodulácia	The process of extracting the information from a modulated carrier wave.
denature (v.)	denaturovať	To add another isotope to a fissile material to make it unsuitable for use in a nuclear weapon.
density	hustota	Symbol r. The mass of a substance per unit of volume. It is measured in kg.m^-3. r = m/V
depleted (adj.)	ochudobnený	Denoting a material that contains less of a particular isotope than it normally contains.
depletion layer	ochudobnená vrstva	A region in a semiconductor that has a lower-than-usual number of mobile charge carriers.
depolarisation	depolarizácia	The prevention of polarization in a primary cell.
derived units	odvodené jednotky	Units defined by means of base units.
detector	detektor	Another term for counter.
deuterium (heavy hydrogen)	deutérium (ťažký vodík)	Symbol D. The isotope of hydrogen. Its nucleus contains one proton and one neutron.
deuteron	deuterón	A nucleus of a deuterium atom consisting of a proton and a neutron bound together.
deviation	odchýlka	The difference between one of an observed set of values and the true value.
device	zariadenie
dew point	rosný bod	The temperature at which the water vapour in the air is saturated.
dextrorotatory	pravotočivý	Denoting a compound that rotates the plane of polarisation of plane-polarised light to the right (clockwise as observed by someone facing the oncoming radiation).
d-form	d-forma	A dextrorotatory form of the isomer.
diamagnetism	diamagnetizmus	Magnetism in which the magnetization is in the opposite direction to that of the applied field, i.e. the susceptibility is negative.
dichroism	dichroizmus	The property of some crystals, such as tourmaline, of selectively absorbing light vibrations in one plane while allowing light vibrations at right angles to this plane to pass through.
dielectric	dielektrikum	A nonconductor of electric charge in which an applied electric field causes a displacement of charge but not a flow of charge.
dielectric constant	relatívna permitivita	Symbol e_r. Former name of relative permitivity.
diffraction	difrakcia (aj ohyb vlnenia)	The spreading or bending of waves as they pass through an aperture or round the edge of a barrier.
diffusion	difúzia (hlavne pre 1) rozptyl (hlavne pre 2)	1. The process by which different substances mix as a result of the random motions of their component atoms, molecules, and ions. 2. The scattering of a beam of light by reflection at a rough surface or by transmission through a translucent (rather than transparent) medium.
difussion cloud chamber	difúzna hmlová komora	A device for making visible the paths of particles of ionising radiation.
digital (adj.)	digitálny	Describing a system in which only whole numbers are handled, normally only two values, corresponding to binary 1 and 0 are used. Compare analogue.
digital-to-analogue converter	digitálno-analógový prevodník	A device that converts digital signals into analogue signals.
dilation	dilatácia	Short for time dilation.
dimension	rozmer
dimensional analysis	rozmerová analýza	A method of checking an equation or a solution to a problem by analysing the dimensions in which it is expressed.
dimensionless (adj.)	bezrozmerný	Describing a quantity that has no dimensions, so is expressed without a unit and has the same numerical value whatever units system is used to calculate it.
diode	dióda	An electronic device with two electrodes that permits flow of current in one direction only.
dioptre	dioptria	Symbol D. A unit for expressing the power of a lens or mirror equal to the reciprocal of its focal length in metres.
dipole	dipól	1. Two equal and opposite charges that are separated by a distance. 2. An aerial commonly used for frequencies below 30 MHz.
direct current (d.c.)	jednosmerný prúd	An electric current in which the net flow of charge is in one direction only. Compare alternating current.
direct-current circuit	obvod jednosmerného prúdu	An electronic circuit with direct current.
directional aerial	smerová anténa	An aerial in which energy is transmitted or received more effectively from some directions than others.
directly heated cathode	priamo-žeravená katóda	A cathode in a thermionic valve that is heated by the current passing through it
discharge	1. výboj 2. vybitie kondenzátora	1. The passage of charge carriers through a gas at low pressure in a discharge tube. 2. The release of electric charge from a capacitor in an external circuit.
discharge tube	výbojová trubica	A tube with a gas at low pressure through which charge carriers are passing and a discharge can occur.
disintegration	premena, rozpad (atómu)	Any process in which an atomic nucleus breaks up spontaneously into two or more fragments in a radioactive decay process or breaks up as a result of a collision with a high-energy particle or nuclear fragment.
dislocation	dislokácia	A defect in the lattice structure of a solid, particularly a metal, that arises if more than one adjacent point defect occurs in a crystal.
dispersion	disperzia (svetla), rozptyl	The splitting up of a ray of light of mixed wavelengths by refraction into its components.
displacement	posunutie	Symbol d. A vector physical quantity connecting the initial and final points of a particle.
displacement (electric flux density)	elektrická indukcia, vektor elektrickej indukcie	Symbol D. The charge per unit area that would be displaced across a layer of conductor placed across an electric field. It is measured in Cm^-2. For isotropic medium: D = eE
dissipative force	disipatívna sila	A force, such as friction, that always opposes the direction of motion, and converts kinetic energy to heat.
distance	dráha	Symbol d or s. The magnitude of displacement d. s = d = \|d\| It is measured (in SI units) in metres (m).
distortion	skreslenie	The extent to which a system fails to reproduce the characteristics of its input in its output.
disturbance	rozruch
divergence (div)	divergencia	Symbol div. The scalar product of the gradient operator Ñ with a vector. For a vector u that has components u₁, u₂, u₃, the divergence is given by: div u = Ñ.u = ¶u₁/¶x + ¶u₂/¶y +¶u₃/¶z
diverging lens	rozptylná šošovka, rozptylka	A lens that can refract or reflect a parallel beam of light into a diverging beam.
diverging meniscus	vypuklodutá šošovka	A type of a diverging lens.
diverging mirror	rozptylné zrkadlo	A mirror that can reflect a parallel beam of light into a diverging beam.
domain	(magnetická) doména	A region within a ferromagnetic material in which all the atomic magnets are aligned in the same direction.
donor	donor	An atom that provides a conduction electron in the doping of a semiconductor to form an n-type semiconductor.
doping	dopovanie, znečistenie prímesami	The addition of small quantities of impurity to a semiconductor to alter its electric properties.
Doppler effect	Dopplerov jav	The apparent change in the observed frequency of a wave as a result of relative motion between the source and the observer.
Doppler shift	Dopplerov posun	The apparent change in wavelength and frequency as a result of relative motion between a wave source and the observer of the wave.
d-orbital	d-orbitál	The third lowest energy orbital for a given principal quantum number. They exist only for principal quantum number of 3 or greater.
dose	dávka	A measure of the extent to which matter has been exposed to ionizing radiation. The SI unit is the gray.
dosimeter	dozimeter	Any device used to measure absorbed dose of ionising radiation.
dot product	skalárny súčin	Colloquial name for the scalar product.
double refraction	dvojitý lom, dvojlom	The property, possessed by certain crystals, of forming two refracted rays from a single incident ray.
down	down, down-kvark, d-kvark	A flavour of quark.
drag	odpor (v aerodynamike)	A dissipative force caused by a solid object moving through a fluid, such as air or water.
drain	drain (elektronika)	The electrode at one end of the channel in a field effect transistor, from which charge carriers leave the channel.
drift velocity	unášavá rýchlosť	The imbalance in speed that causes charge carriers to produce a net flow of charge through a conductor.
dry cell	suchý článok	A primary or secondary cell in which the electrolytes are in the form of a paste.
Dulong and Petit’s law	Dulongov-Petitov zokon	For a solid element the product of the relative atomic mass and the specific heat capacity is a constant equal to about 25 Jmol^-1K^-1.
dwarf star	trpasličia hviezda	A star, such as the sun, that lies on the main sequence in a Hertzsprung-Russel diagram.
dynamic equilibrium	dynamická rovnováha	An equilibrium in which activity in one sense or direction is in aggregate balanced by comparable reverse activity.
dynamics	dynamika	The branch of mechanics concerned with the motion of bodies under the action of forces.
dyne	dyn	The unit of force in the c.g.s. system. 1 dyne = 10^-5 N
early universe	raný vesmír	The study of cosmology at the time very soon after the big bang.
earth	Zem	The planet that orbits the Sun between planets Venus and Mars at a mean distance from the Sun of 149 600 000 km.
earth’s atmosphere	zemská atmosféra, atmosféra Zeme	The gas that surrounds the earth. The earth’s atmosphere has a thickness of approximately 400 km but its density decreases with height. It is divided into the following layers: (1) troposphere (7 km at the poles / 28 km at the equator) (2) stratosphere (50 km) (3) ionosphere (400 km) (4) exosphere (above 400 km)
earth’s magnetic field	zemské magnetické pole, magnetické pole Zeme	The magnetic field generated by the Earth’s magnetic poles.
earthed	uzemnený	Connected with earth or any point with the electric potential equal to the potential of earth.
echo	ozvena	The reflection of a wave by a surface or object so that a weaker version of it is detected shortly after the original.
eclipse	zatmenie	The total or partial obscuring of light from a celestial body as it passes behind or through the shadow of another body.
ecliptic	ekliptika	The path traced out by the Sun against the background stars as a result of the Earth’s orbit around the Sun. Seen from the earth, the sun appears to move around the ecliptic once every year.
eddy current	vírivý prúd	A current induced in a conductor situated in a changing magnetic field or moving in a fixed one.
effective value	efektívna hodnota	A typical value of a continuously varying quantity, such as alternating electric current, obtained similarly from many samples taken at regular time intervals during a cycle.
efficiency	účinnosť	A measure of the performance of a machine, engine, etc., being the ratio of the energy or power it delivers to the energy or power fed to it.
Einstein equation	Einsteinova rovnica	E = mc²
Einstein shift	Einsteinov posun	A displacement of spectral lines towards the red caused not by a Doppler effect but by a high gravitational field. Also known as Einstein redshift.
elastic collision	pružná zrážka	A collision in which the total kinetic energy of the colliding bodies after collision is equal their total kinetic energy before collision.
elastic limit	medza pružnosti	The maximum strain that can be applied to an elastic material beyond which the material does not return to its original length when the stretching force is removed.
elastic modulus	modul pružnosti	The ratio of the stress applied to a body to the strain produced. E = s/e where e = Dl/l₀ (longitudinal strain) - see Young modulus of elasticity, or e = DV/V₀ - see bulk modulus.
elasticity	pružnosť	The property of certain materials that enables them to return to their original dimensions after an applied stress has been removed. In general, if a stress is applied to a wire, the strain will increase in proportion until a certain point called the limit of proportionality is reached.
electric arc	elektrický oblúk	A luminous discharge between two electrodes.
electric charge	elektrický náboj	See charge.
electric constant	elektrická konštanta (zastaralo: permitivita vákua)	e₀ = 8.854 x 10^-12 Fm^-1.
electric current	elektrický prúd	Symbol I. The flow of electric charge through a conductor. It is measured in amperes (A).
electric displacement	elektrická indukcia, vektor elektrickej indukcie	Symbol D. The charge per unit area that would be displaced across a layer of conductor placed across an electric field. It is measured in Cm^-2. For isotropic medium: D = eE where e is permitivity and E is electric intensity.
electric field	elektrické pole	A region in which an electric charge experiences a force usually because of a distribution of other charges. An electric field can also be created by a changing magnetic field.
electric field lines	siločiary elektrického poľa	Lines drawn on a diagram that show the direction of the force on a positively charged particle placed at that point in an electric field.
electric field strength	intenzita elektrického poľa	Symbol E. Electric intensity at any point in an electric field is defined as the force per unit charge experienced by a small charge placed at that point. It is measured in volts per metre (Vm^-1).
electric flux	elektrický tok	Symbol y. In an electric field, a measure of the total amount of electric field passing through an area. If the electric field strength is E, and it passes through area S at an angle a, then the electric flux is y = E.S.cos a
electric flux density	hustota elektrického toku	An obsolete term for electric displacement.
electric intensity	intenzita elektrického poľa	Symbol E. Electric intensity at any point in an electric field is defined as the force per unit charge experienced by a small charge placed at that point. It is measured in volts per metre (Vm^-1).
electric motor	elektromotor	A machine for converting electrical energy into mechanical energy.
electric polarization	elektrická polarizácia, vektor elektrickej polarizácie	Symbol P. The stress within the dielectric caused by applied electric field. P = D - e₀E, where D is the displacement, E is the electric field strength, and e₀ is the electric constant.
electric potential	elektrický potenciál	Symbol φ. The energy (W) required to bring unit electric charge (Q) from infinity to the point in an electric field at which the potential is being specified. φ = W/Q The unit of electric potential is the volt (V).
electric power	výkon jednosmreného/striedavého prúdu, elektrický výkon	The rate of expending energy or doing work in an electrical system. For a direct-current circuit: P = UI, for alternating-current circuit: P = UIcos φ
electric spark	elektrická iskra	The transient passage of an electric current through a gas between two pints of high opposite potential, with the emission of light and sound.
electric susceptibility	elektrická susceptibilita	Symbol χ_e. The dimensionless quantity referring to a dielectric equal to P/e₀E, where P is the electric polarization, E is the electric intensity producing it, and e₀ is the electric constant.
electrical conduction	vedenie elektrického prúdu	The passage of electric charge through a substance under the influence of an electric field.
electrical conductivity	merná electrická vodivosť	Symbol g. The reciprocal of resistivity (r) g = 1/r = l/(R.S) It is measured in siemens per metre (S.m^-1).
electrical energy	elektrická energia	A form of energy related to the position of an electric charge in an electric field. For a body with charge Q and an electric potential φ, its electrical energy is E = Qφ.
electricity	elektrina, elektrický prúd (ako jav, nie veličina)	Any effect resulting from the existence of stationary or moving electric charges.
electrochemical equivalent	elektrochemický ekvivalent	Symbol z. The mass (m) of a given element liberated from a solution of its ions in electrolysis by one coulomb of charge (Q) z = m/Q. It is measured in kg.C^-1.
electrode	elektróda	A conductor that emits or collects electrons in a cell, thermionic valve, semiconductor device, etc.
electrodynamics	elektrodynamika	The study of electric charges in motion, the forces created by electric and magnetic fields, and the relationship between them.
electrolysis	elektrolýza	The production of a chemical reaction by passing an electric current through an electrolyte. Positive ions migrate to the cathode and negative ions to the anode.
electrolyte	elektrolyt	A liquid that conducts electricity as a result of the presence of positive or negative ions.
electrolytic capacitor	elektrolytický kondenzátor	Capacitor in which the dielectric is formed by electrolysis.
electrolytic cell	elektrolytický článok	A cell in which electrolysis occurs; i.e. one in which current is passed through the electrolyte from an external source.
electrolytic rectifier	elektrolytický usmerňovač	A rectifier consisting of two dissimilar electrodes immersed in an electrolyte.
electromagnet	elektromagnet	A magnet consisting of a soft ferromagnetic core with a coil of insulated wire wound round it.
electromagnetic induction	elektromagnetická indukcia	The production of an electromotive force in a conductor when there is a change of magnetic flux linkage with the conductor or when there is relative motion of the conductor across a magnetic field.
electromagnetic interaction	elektromagnetická interakcia	One of the four fundamental interactions which is responsible for the forces that control atomic structure, chemical reactions, and all electromagnetic phenomena. It accounts for the forces between charged particles, but unlike the gravitational interaction, can be either attractive or repulsive.
electromagnetic radiation	elektromagnetické žiarenie	Energy resulted from the acceleration of electric charge and the associated electric fields and magnetic fields. The energy can be regarded as waves propagated through space involving oscillating electric and magnetic fields.
electromagnetic spectrum	elektromagnetické spektrum	The range of wavelengths over which electromagnetic radiation extends.
electromagnetic wave	elektromagnetická vlna, elktromagnetické vlnenie	Waves of energy composed of oscillating electric and magnetic fields, in phase but at right angles t one another, propagating through space as a transverse wave.
electromotive force (e.m.f.)	elektromotoricke napatie	The greatest potential difference that can be generated by a particular source of electric current.
electron	elektrón	An elementary particle, classed as a lepton, with a negative charge of 1.60217733 x 10^-19 C.
electron capture	elektrónový záchyt	A radioactive transformation in which a nucleus acquires an electron from an inner orbit of the atom, thereby transforming, initially, into a nucleus with the same mass number but an atomic number one less than that of the original nucleus.
electron diffraction	elektrónová difrakcia	Diffraction of a beam of electrons by atoms or molecules.
electron gun	elektrónové delo	A device used in cathode-ray tubes, electron microscopes, etc., to produce a steady narrow beam of electrons.
electron microscope	elektrónový mikroskop	A form of microscope that uses a beam of electrons instead of a beam of light to form a large image of a very small object.
electron-hole pair	pár voľný elektrón-diera	An electron and a hole produced at a point in a semiconductor.
electronics	elektronika	The study and design of control, communication, and computing devices that rely on the movement on electrons in circuits containing semiconductors, resistors, capacitors, and inductors.
electronvolt	elektrónvolt	Symbol eV. A unit of energy equal to the work done on an electron in moving it through a potential difference of one volt. 1 eV = 1.602 x 10^-19J
electroscope	elektroskop	A device for detecting electrical charge and for identifying its polarity.
electrostatic field	elektrostatické pole	The electric field that surrounds a stationary charged body.
electrostatics	elektrostatika	The study of electric charges at rest, the forces between them, and the electric fields associated with them.
electrostriction	elektrostrikcia	A change in the dimensions of a body as a result of reorientation of its molecules when it is placed in an electric field.
electroweak interaction	elektroslabá interakcia	The single interaction that unified electromagnetic and weak interactions, suggested by the physicists S.L.Glashow, S.Weinberg and A.Salam The electroweak interaction is mediated by photons and by intermediate vector bosons, called the W boson and the Z boson.
electroweak theory	elektroslabá teória	A gauge theory that gives a unified description of the electromagnetic and weak interactions.
element	prvok	A substance that cannot be broken down into more fundamental constituents by normal chemical means, being made of atoms all of the same type (i.e. having the same atomic number).
elementary particles	elementárne častice	The fundamental constituents of all the matter in the universe. See table of elementary particles (standard model).
elliptical galaxy	eliptická galaxia	Galaxy that appears like ellipsoidal cloud of stars, with very little internal structure apart from (in some cases) a denser nucleus.
emission spectrum	emisné spektrum	A spectrum produced as excited atoms or molecules return to lower energy levels, giving off electromagnetic radiation of specific wavelengths, with all other wavelengths being absent.
emitter	emitor	The electrode in a junction transistor from which charge carriers are injected into the base before arriving at the collector.
energy	energia	A measure of a system’s ability to do work. It is measured in joules (J).
energy band	pásmo energie, energetické pásmo	A range of energies that electrons can have in a solid.
energy barrier	energetická bariéra	The amount of energy that may need to be provided before a physical or chemical process can take place, even though the process as a whole may release energy.
energy level	hladina energie, energetická hladina	A definite fixed energy that a system described by quantum mechanics, such as molecule, atom, electron, or nucleus, can have.
engine	motor, stroj	Any device for converting some forms of energy by mechanical work.
enthalpy	entalpia	Symbol H. A thermodynamic property of a system defined by H = U + pV, where U is the internal energy of the system, p its pressure, and V its volume.
entropy	entropia	Symbol S. A measure of the unavailability of a system’s energy to do work. In a wider sense, entropy can be interpreted as a measure of disorder; the higher the entropy, the greater the disorder. Thus S = k.ln W, where k is the Boltzmann constant and W is the number of ways in which the molecules in the system can be arranged to produce the specified state.
equation of motion (kinematic equation)	pohybová rovnica	Any of four equations that apply to bodies moving linearly with uniform acceleration (a). The equations, which relate distance covered (s) to the time taken (t), are: v = v₀ + at s = (v₀ + v)t/2 s = v₀t + at²/2 v² = v₀² + 2as where v₀ is the initial velocity of the body and v its final velocity.
equation of state	stavová rovnica	An equation that relates the pressure p, volume V, and thermodynamic temperature T of an amount of substance n. The simplest is the ideal gas law: pV = nRT where R is the universal gas constant.
equilibrium	rovnovážny stav, rovnováha	A state in which a system has its energy distributed in the statistically most probable manner; a state of a system in which forces, influences, reactions, etc., balance each other out so that there is no net change.
equipartition of energy	ekvipartícia energie, ekvipartičná teoréma	The principle that states that thermal energy will be distributed equally between the available degrees of freedom, the average energy for each degree of freedom being kT/2, where k is the Boltzmann constant and T is the thermodynamic temperature.
equipotential	ekvipotenciála	A line joining points that are at the same electric potential.
equivalence of mass and energy	ekvivalencia hmotnosti a energie	The concept that when an object gains energy, in whatever form, it gains mass. This is summed up in the Einstein equation E = mc².
erect image	priamy obraz
Esaki diode	Esakiho dióda	A semiconductor diode based on the tunnel effect.
escape velocity	úniková rýchlosť	The minimum speed needed by an object (e.g. space vehicle) to escape from the gravitational field of a celestial body (e.g. earth, moon, etc.) from which it was launched.
ether	éter	A hypothetical medium once believed to be necessary to support the propagation of electromagnetic radiation.
evaporation	vyparovanie	The change of state of a liquid into a vapour at a temperature below the boiling point of the liquid occurring at the surface of the liquid.
even-even nucleus	párno-párne jadro	An atomic nucleus containing an even number of protons and an even number of neutrons.
even-odd nucleus	párno-nepárne jadro	An atomic nucleus containing an even number of protons and an odd number of neutrons.
event horizon	udalostný horizont	For a black hole, the surface on which the escape velocity is equal to the speed of light.
exchange force	výmenná sila	A force resulting from the continued interchange of particles in a manner that bonds their hosts together.
excitation	excitácia	A process in which a nucleus, electron, atom, ion, or molecule acquires energy that raises it to a quantum state (excited state) higher than that of its ground state.
excited state	excitovaný stav	A quantum state (in a nucleus, electron, atom, ion, or molecule) with an energy higher than the lowest allowed energy (ground state).
exclusion principle	vylučovací princíp	Short for Pauli exclusion principle.
exosphere	exosféra	Layer of the earth’s atmosphere.
expand (v.)	rozpínať sa, rozťahovať sa, predlžovať sa
expansion	rozťažnosť	An increase in size, particularly as a result of an increase in temperature.
expansion of the universe	rozpínavosť vesmíru	The hypothesis, based on the evidence of the redshift, that the distance between the galaxies is continuously increasing.
expansivity	koeficient teplotnej rozťažnosti	Common term for linear, superficial, and volume expansivity. A measure of the increase in length (linear expansivity), area (superficial expansivity) , or volume (bulk expansivity) of a material when it is heated. l = l₀(1 + aDt) S = S₀(1 + bDt) V = V₀(1 + gDt) with a,b, and g being the linear, superficial and volume coefficients of expansion respectively.
experiment	pokus
external	vonkajší
extraordinary ray	mimoriadny lúč	In double refraction, the second refracted ray that does not obey the normal laws of refraction.
extremely high frequency (EHF)	extrémne vysoká frekvencia	A radio frequency between 30 GHz and 300 GHz.
extrinsic semiconductor	nevlastný polovodič, primesový polovodič	A semiconductor in which the type of conduction that predominates depends on the number and valence of the impurity atoms present.
eye lens, lens	očná šošovka	Part of a human eye.
eyepiece	okulár	The lens or system of lenses in an optical instrument that is nearest to the eye. It usually produces a magnified image of the previous image formed by the instrument.
f.p.s. units	jednotky f.p.s.	The British system of units based on foot (ft), pound (lb), and second (s). 1 ft = 0.3048 m 1 lb = 0.45359237 kg
Fabry-Pérot interferometer	Fabryho-Perotov interferometer	A type of interferometer in which monochromatic light is passed through a pair of parallel half-silvered glass plates producing circular interference fringes.
face-centred cubic (f.c.c.)	plošne centrovaná elementárna bunka	One of packings of cubic crystal. See also cubic close packed; cubic crystal.
Fahrenheit scale	Fahrenheitova stupnica	A temperature scale in which the temperature of boiling water is taken as 212 degrees and the temperature of melting ice as 32 degrees.
fall-out	(rádioaktívny) spád	Radioactive particles deposited from the atmosphere either from a nuclear explosion or from a nuclear accident.
farad	farad	Symbol F. The SI unit of capacitance. 1 F = 1 CV^-1.
Faraday cage	Faradayova klietka	An earthed screen made of metal wire that surrounds an electric device in order to shield it from external electrical fields.
Faraday constant	Faradayova konštanta	Symbol F. The electric charge carried by one mole of electrons F = 9.6485309 x 10⁴ C.mol^-1
Faraday effect	Faradayov jav	The rotation of the plane of polarization of electromagnetic radiation on passing through an isotropic medium exposed to a magnetic field.
Faraday’s laws of electrolysis	Faradayove zákony elektrolýzy	The laws describing electrolysis: (1) The amount of chemical change during electrolysis is proportional to the charge passed. (2) The charge required to deposit or liberate a mass m is given by Q = Fmz/M, where F is the Faraday constant, z the charge of the ion, and M the relative ionic mass.
Faraday’s laws of electromagnetic induction	Faradayove zákony elektromagnetickej indukcie	(1) An e.m.f. is induced in a conductor when the magnetic field surrounding it changes. (2) The magnitude of the e.m.f. is proportional to the rate of change of the field. (3) The sense of the induced e.m.f. depends on the direction of the rate of change of the field.
fast breeder reactor	rýchly množivý reaktor	A nuclear reactor in which there is no moderator, the temperature is higher and a liquid-metal coolant is used. It produces the same fissile material as it uses.
fast neutron	rýchly neutrón	A neutron resulting from nuclear fission that has an energy in excess of 0.1 MeV, having lost little of its energy by collision.
fast reactor	rýchly reactor	A nuclear reactor in which there is no moderator, the temperature is higher and a liquid-metal coolant is used, usually liquid sodium.
feedback	spätná väzba	The use of part of the output of a system to control its performance
Fermat’s principle	Fermatov princíp	The path taken by a ray of light between any two points in a system is always the path that takes the least time.
Fermi distribution	Fermiho rozdelenie (energií)	A mathematical description of the energies of fermions. Unless the temperature is very high, all the energy levels from zero up to a fixed maximum, called the Fermi energy, are filled whilst the rest are empty.
Fermi energy	Fermiho energia	The energy up to which energy levels are filled in the Fermi distribution. It is the energy at which the probability of an energy level being occupied is ½.
Fermi level	Fermiho energia.	Same as Fermi energy.
Fermi-Dirac statistics	Fermi-Diracova štatistika	Quantum statistics that apply if only one particle may occupy each quantum state. The particles are called fermions. Fermions have a total angular momentum (n + ½)h and any wave function that involves identical fermions is always antisymmetric.
fermion	fermión	An elementary particle (or bound state of an elementary particle, e.g. an atomic nucleus or an atom) with half-integral spin; i.e. a particle that conforms to Fermi-Dirac statistics. Compare boson.
ferrimagnetism	ferimagnetizmus	A special form of antiferromagnetism, a type of magnetism exhibited by the ferrites.
ferrite	ferit	A member of a class of mixed oxides MO.Fe₂O₃, where M is a metal such as cobalt, manganese, nickel, or zinc. The ferrites are ceramic materials that show either ferrimagnetism or ferromagnetism, but are not electrical conductors.
ferromagnetism	feromagnetizmus	Type of magnetism. In ferromagnetic substances, within a certain temperature range, there are net atomic magnetic moments, which line up in such a way that magnetization persists after the removal of the applied field.
fertile material	množivý materiál	A nuclide that can absorb a neutron to form a fissile material.
fibre optic	optické vlákno	A solid glass or plastic fibre, typically thinner than the thickness of a human hair, that can transmit light. The light does not leave the fibre when it hits the edge, but passes along the fibre by the process of total internal reflection.
field	pole	A region in which a body experiences a force as the result of the presence of some other body or bodies.
field magnet	poľový magnet	The magnet that provides the magnetic field in an electrical machine.
field of force	silové pole	A field characterised by a specific force.
field-effect transistor (FET)	tranzistor riadený poľom	An electronic device similar in its uses to a junction transistor, but constructed in a different way. A field effect transistor has a channel of semiconducting material along with a current flows between terminals called the source and the drain. A third electrode, called the gate, is formed either on an insulating layer (in an IGFET - insulated gate FET) or from a reverse biased PN junction diode (JFET - junction FET).
filter	filter	A device placed in the path of a beam of radiation to alter its frequency distribution.
finder	hľadáčik	A small low-powered astronomical telescope, with a wide filed of view, that is fixed to a large astronomical telescope so that the large telescope can be pointed in the correct direction to observe a particular celestial body.
first law of thermodynamics	prvý termodynamický zákon	When heat is supplied to an isolated system, the amount of heat energy, DQ, equals the increase in internal energy, DU, plus the mechanical work, DW, done by the system: DQ = DU + DW
fissile material	štiepny materiál	A nuclide of an element that undergoes nuclear fission, either spontaneously or when irradiated by neutrons.
fission	štiepenie	Short for nuclear fission.
fission products	produkty štiepenia	Parts that have been produced by splitting a heavy nucleus in a nuclear reaction.
fixed point	fixný bod	A temperature that can be accurately reproduced to enable it to be used as the basis of a temperature scale.
fixed star	stálica	One of very many heavenly bodies that does not appear to alter its position on the celestial sphere.
flavour	vôňa	The property that distinguishes one type of quark from another. The six flavours of quark, which make up the standard model, of particle physics, are up, down, strange, charm, top and bottom.
flip-flop (bistable circuit)	(bistabilný) klopný obvod	An electronic circuit that has two stable states.
fluid	tekutina	Any substance that can flow - gas and liquid.
fluid mechanics	mechanika tekutín	The study of the fluids at rest and in motion.
flux	tok	Short for luminous flux or electric flux or magnetic flux.
flux density	hustota toku	Short for electric flux density or magnetic flux density.
focal length	ohnisková vzdialenosť	Symbol f. The distance between the optical centre of a lens or pole of a spherical mirror and its principal focus.
focal point	ohniskový bod	See focus.
focus	ohnisko	Any point in an optical system through or towards which rays of light are converged.
foot	stopa	Symbol ft. The unit of length in f.p.s. units 1 ft = 1/3 yd = 0.3048 m
forbidden band	zakázané pásmo	Energy band between valence band and conduction band which is not allowed.
force	sila	Symbol F. Any agency that tends to change the state of rest or motion of a body; i.e. one that tends to cause a body to accelerate. Force is defined as being proportional to the rate of change of momentum of a body. It is a vector quantity, and the SI unit of force is the newton (N).
forward-biased	priepustný smer, zapojený v priepustnom smere	Describing a pn junction to which a voltage is applied enabling charge carriers to carry current across the junction. Compare reverse-biased.
fovea	žltá škvrna	Part of a human eye.
frame of reference	vzťažná sústava	A set of directions in space and time together with a reference point called an origin. The position of any other point is described by how far away it is from the origin in each of the directions.
free electron	voľný elektrón	An electron in metal or semiconductor that is not bound to any single atom but is free to move, carrying its charge and energy through the material.
free energy	voľná energia	A measure of system’s ability to do work.
free fall	voľný pád	Motion resulting from a gravitational field that is unimpeded by a medium that would provide a frictional retarding force or buoyancy. In the earth’s gravitational field, free fall takes place at a constant acceleration, known as the acceleration of free fall.
free space	voľný priestor	A region in which there is no matter and no electromagnetic or gravitational fields.
frequency	frekvencia	Symbol f. The rate of repetition of a regular event. The number of cycles of a wave, or some other oscillation or vibration, pre second is expressed in hertz (Hz).
frequency modulation	frekvenčná modulácia	A type of modulation system in which the frequency of a carrier wave is varied, to convey information such as a speech or music signal. Frequency modulation requires a wider bandwidth than amplitude modulation.
frequency range	frekvenčný rozsah	An interval where a frequency can be.
friction	trenie, trecia sila	The force that resists the motion of one surface to another with which it is in contact.
full-wave rectifier	dvojcestný usmerňovač	A rectifier in which both half-waves are rectified.
fundamental constants	fundamemntálne konštanty, univerzálne konštanty	Those parameters that do not change throughout the universe.
fundamental frequency	základná frekvencia	The smallest frequency of a sinusoidal oscillation, called also the first harmonic, of a system that supports standing waves, defined as f = v/λ = v/2l, where v the speed of the stationary wave, λ its wavelength, and l the length of the string.
fundamental interactions	fundamentálne interakcie	The four different types of interaction that can occur between bodies. These interactions can take place even if the bodies are not in physical contact and together they account for all the observed forces that occur in the universe. The fundamental interactions are: (1) gravitational interaction (2) weak interaction (3) electromagnetic interaction (4) strong interaction
fundamental units	fundamentálne jednotky	A set of independently defined units of measurement that forms the basis of a system of units. Such a set requires three mechanical units (usually length, mass, and time) and, in some systems, one electrical unit. In the metric system the centimetre-gram-second (c.g.s.) system was replaced by the metre-kilogram-second (m.k.s.) system which provides the basis for SI units. In British Imperial units the foot-pound-second (f.p.s.) system was formerly used.
fuse	poistka	A safety device that uses the heating effect of an electric current to protect an electrical device or circuit from overloading.
fusion	syntéza	Short for nuclear fusion.
fusion reactor	termonukleárny reaktor (aj fúzny reaktor)	Same as thermonuclear reactor.