radar

radar

Acronym of radio detection and ranging. The process or system based on the reflection of microwaves for the detection of objects that reflect microwaves, particularly ships and aircraft.

radian

radián

Symbol rad. The SI unit of plane angle. One radian is the angle subtended at the centre of a circle by an arc of equal length to the radius.

radiant energy

radiačná energia

Energy transmitted as electromagnetic radiation.

radiant flux

žiarivý tok

Φ_e = dE / dt. Measured in watts.

radiant intensity

žiarivosť

Symbol I_e. The radiant flux per unit solid angle emitted by a point source.

I_e = dΦ_e/dΩ

It is measured in watts per steradian (W.sr^-1).

radiation

1. žiarenie

2. žiarenie, radiácia

1. Energy travelling in the form of electromagnetic waves or photons.

2. A stream of particles, especially alpha- or beta-particles from a radioactive source or neutrons from a nuclear reactor.

radiation detector

detektor žiarenia

Any device for detecting ionising radiation by the ionisation it produces.

radio frequencies

rádiofrekvencie

The range of frequencies, between about 3 kHz and 300 GHz, over which electromagnetic radiation is used in radio transmission. It is subdivided into 8 equal bands:

radio telescope

rádioteleskop

An instrument for detecting and measuring electromagnetic radiation of radio frequencies that have passed through the radio window in the earth’s atmosphere and reached the surface of the earth.

radio transmission

The transmission of radio waves from a transmitting aerial to a receiving aerial

radio waves

rádiové vlny

Electromagnetic waves with a wavelength in the range of 1 mm to 100 km, used in communication - radar, television, and radio broadcasting.

radioactivity

rádioaktivita

The spontaneous disintegration of certain atomic nuclei accompanied by the emission of alpha-particles (helium nuclei), beta-particles (electrons), or gamma-radiation (short-wave electromagnetic waves).

radiocarbon dating

určenie veku rádiouhlíkovou analýzou

Same as carbon dating.

radionuclide

rádionuklid

A nuclide that is radioactive.

radius of curvature

polomer krivosti

The radius of the sphere part of which is formed by a lens surface or curved mirror.

rationalised Planck constant

racionalizovaná Planckova konštanta (h trans)

ħ = h/2π = 1.054589 x 10^-34 Js,

where h is the Planck constant.

ray

lúč

An infinitely narrow, parallel-sided beam of radiation, such as light, or a line drawn to represent such a beam.

Rayleigh-Jeans formula

Rayleigho-Jeansov vyžarovací zákon

The law giving the distribution of energy radiated by a black body, but only for low frequencies (f << kT/h):

E_f = 2c^-2f²kT,

where E_f is the monochromatic specific intensity, c is the speed of light, k is the Boltzmann constant.

reactance

reaktancia

Symbol X. A property of a circuit containing inductance (X_L) or capacitance (X_C) that together with any resistance (R) makes up its impedance.

X = X_L - X_C.

The impedance Z is given by

Z² = R² + X².

Reactance is measured in ohms.

reaction

reakcia

See Newton’s laws of motion

real image

skutočný obraz

The image through which the rays of light actually pass.

rectification

usmernenie

The process of obtaining a direct current from an alternating electrical supply.

rectifier

usmerňovač

An electrical device that allows more current to flow in one direction than the other, thus enabling alternating current  e.m.f. to drive only direct current.

red giant

červený obor

A giant cool star that is at its late stage of stellar evolution.

redshift

červený posun

A displacement of the lines in the spectra of certain galaxies towards the red end of the visible spectrum (i.e. towards longer wavelengths).

It is caused by the Doppler effect or by a high gravitational field (see Einstein redshift).

Doppler redshift results from the recession of the galaxies along the line of sight (see expansion of the universe).

Einstein redshift is caused by a high gravitational field. Some astronomers believe that this is the cause of the large redshifts of quasars.

reference body

vzťažné teleso

reference point

vzťažný bod

reflection

odraz

The return of all or part of a beam of particles or waves when it encounters the boundary between two media.

refraction

lom

The change of direction suffered by wavefront as it passes obliquely from one medium to another in which its speed of propagation is altered.

refractive index (pl. indices)

index lomu

Symbol n. The refractive index of a medium is the ratio of the speed of electromagnetic radiation in free space (c) to the speed of the radiation in that medium (v)

n = c/v.

As the refractive index varies with wavelength, the wavelength should be specified.

refractometer

refraktometer

Any of various instruments for measuring the refractive index of a substance or medium.

relative atomic mass (r.a.m.)

relatívna atómová hmotnosť

Symbol A_r. The ratio of the average mass per atom of the naturally occurring form of an element to 1/12 of the mass of a carbon-12 atom.

relative permeability

relatívna permeabilita

Symbol m_r. The relative permeability of a substance is given by

m_r = m/m₀,

where m is the permeability of the medium and , m₀ is the magnetic constant (permeability of free space).

relative permitivity

relatívna permitivita

Symbol e_r. The relative permitivity (e_r) of a medium is given by

e_r = e/e₀,

where e is the permitivity of the medium and e₀ is the electric constant (permitivity of free space).

relativistic mass

relativistická hmotnosť

m = m₀.Ö(1 - v²/c²),

where m₀ is the rest mass of a body moving at speed v, and c is the speed of light.

relativistic mechanics

relativistická mechanika

An extension of Newtonian mechanics that takes into account the theory of relativity.

relativistic speed

relativistická rýchlosť

A speed that is sufficiently large to make the mass of a body significantly greater than its rest mass.

relativity

relativita

A blanket term covering the relativity principle, special theory of relativity and general theory of relativity. See also Galilean relativity.

relativity principle

princíp relativity

The idea that there is no observer who has a privileged viewpoint and can claim to be truly at rest. Thus a view of events seen by any observer is equally valid, and all velocities are relative to a given observer.

repel (v.)

odpudzovať (sa)

resistance

odpor (pre jednosmerne obvody)

rezistancia (pre striedave obvody)

Symbol R. The ratio of the potential difference (U) across the electrical component to a current (I) passing through it.

R = U/I.

It is measured in ohms (Ω).

resistivity

merný elektrický odpor

Symbol ρ. The resistance between opposite faces of a material 1 metre long with the cross-section area of 1m².

For a conductor of length l with cross-sectional area S and resistivity ρ, the resistance is given by

R = ρl/S.

Resistivity is measured in ohm meters (Ωm).

resistor

rezistor, odpor (ako súčiastka)

A component in an electrical or electronic circuit that is present because of its electrical resistance.

resonance

rezonancia

An oscillation of a system at its natural frequency of vibration, as determined by the physical parameters of the system.

resonance circuit

rezonančný obvod

A reactive circuit (see reactance) so arranged that it is capable of resonance.

rest energy

pokojová energia

E₀ = m₀c²,

where m0 is the rest mass and c the speed of light.

rest mass

pokojová hmotnosť

Symbol m₀. The mass of a body at rest when it measured by an observer who is at rest in the same frame of reference.

retina

sietnica

Part of a human eye.

reverse piezoelectric effect

obrátený piezoelektrický jav

If the opposite faces of a piezoelectric crystal are subjected to a potential difference, the crystal changes its shape.

reverse-biased

záverný smer, zapojený v závernom smere

Describing the state of a PN junction diode when a voltage is applied that tends to increase the size of the depletion layer. In this state, no current can flow. Compare forward-biased.

revolve (v.)

otáčať sa, rotovať

rheostat

reostat

The way of connecting a variable resistor in an electrical circuit so that we can change its resistance from the range of 0 to the maximum resistance of the variable resistor, i.e. we can set the resistor to have any value of resistance between 0 and R ohms, where R is the maximum resistance of the resistor.

rods

tyčinky

A type of light-sensitive receptor cells present in the retina of human eye. They are essential for vision in dim light. Compare cones.

rotational motion

otáčavý pohyb

A motion of a body about a specified axis in which all the points of the body describe the circles (or parts of the circles) with their centres being at the axis of rotation and the circles lie in the planes perpendicular to the axis of rotation. Compare translation motion.

Rydberg constant

Rydbergova konštanta

R = μ₀²m_ee⁴c³/8h³,

where μ₀ is the magnetic constant (permeability of free space), m_e is the mass of an electron, e is the charge of an electron, c is the speed of light, and h is the Planck constant.

It has the value 1.097 x 10⁷ m^-1.

saturated vapour

nasýtená para

The state of a vapour whose partial pressure is equal to its saturated vapour pressure, the maximum density that the vapour can have at that temperature. If a saturated vapour is cooled, the liquid will condense.

sawtooth waveform

pílovité kmity

A waveform in which the variable increases uniformly with time for a fixed period, drops sharply to its initial value, and then repeats the sequence periodically.

scalar product

skalárny súčin

The product of two vectors u and v, with components u₁, u₂, u₃ and v₁, v₂, v₃, respectively, given by

u.v = u₁v₁ + u₂v₂ + u₃v₃.

scale

stupnica (napr. teplomera)

scattering of electromagnetic radiation

rozptyl elektromagnetického žiarenia

The process in which electromagnetic radiation is deflected by particles in the matter through which it passes.

Schrödinger equation

Schrödingerova rovnica

An equation used in wave mechanics for the wave function of a particle

The time-independent Schrödinger equation is:

(-(h²/2m)Δ + U)ψ = Eψ,

where ψ is the wave function, h is the Planck constant, Δ is the Laplace operator, m the particle’s mass, E its total energy, and U its potential energy.

The time-dependent Schrödinger equation is:

iħ.δψ/δt = (-(h²/2m)Δ + U)ψ,

where i is the imaginary unit (i² = -1), and ħ the rationalised Planck constant.

sclerotic

očné bielko

Part of a human eye.

screw

skrutka

One of the six simple machines.

second

sekunda

Symbol s. The SI unit of time. One second is time equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom.

secondary cell

sekundárny článok

A voltaic cell in which the chemical reaction producing the e.m.f. is reversible and the cell can therefore be charged by passing a current through it. Compare primary cell.

secondary colour

sekundárna farba

Any colour that can be obtained by mixing two primary colours.

secondary wavelet

elementárne vlnoplochy (pri Huygensovom princípe)

A small section of wavefront used to predict the position of the next wavefront in Huygens’ construction.

secondary winding

sekundárne vinutie

The winding on the output side of a transformer or induction coil. Compare primary winding.

self-inductance

(vlastná) indukčnosť

Symbol L. A measure of the effect in which a changing current in a coil causes an e.m.f. in the same coil, tending (by Lenz’s law) to oppose the change in current. The SI unit of self-inductance is henry (H).

semiconductor

polovodič

A crystalline solid, such as silicon, with an electrical conductivity (typically 10⁵ - 10^-7 Sm^-1) intermediate between that of a conductor and an insulator. Semiconductor is nonconductive at the absolute zero temperature.

semiconductor diode

polovodičová dióda

A diode with a pn junction, made from semiconductors.

series circuit

sériový obvod

A circuit in which circuit elements are arranged in sequence so that the same current flows through each of them in turn.

shell

elektrónová vrstva, vrstva, sféra

A series of atomic orbitals of roughly similar energies. The shells are labelled K, L, M, N, O, P. The K-shell is closest to the nucleus and can hold 2 electrons. The n-th shell out from the nucleus can hold 2n² electrons.

SI units

jednotky SI

(Systeme International d’Unites)

The international system of units now recommended for most scientific purposes. The system has 7 base units and 2 supplementary units. See the table of SI units.

sideband

postranné pásmo

The band of frequencies above or below the frequency of the carrier wave in a telecommunications system within which the frequency components of the wave produced by modulation fall.

sidereal day

sideriálny deň

The day measured with respect to the fixed stars and is 4.09 minutes shorter than the mean solar day as a result of the imposition of the earth’s orbital motion on its rotational motion.

sidereal year

sideriálny rok

The average period of revolution of the Earth with respect to the fixed stars; it is 365.256 mean solar days.

siemens

Siemens

Symbol S. The SI unit of electrical conductance.

sign convention

znamienková dohoda

A set of rules determined by convention for giving plus or minus signs to distances in the formulae involving lenses and mirrors.

simple cubic

primitívna (prostá) ementárna bunka

See cubic close packed; cubic crystal.

simple harmonic motion (SHM)

jednoduchý kmitavý pohyb, harmonický pohyb

An oscillating motion of an object or system about a fixed point such that the acceleration of the object is always directed to the fixed point and is proportional to the displacement from the fixed point.

If acceleration is a, the displacement is x and the angular frequency ω, then

a = -ω²x.

simple machine

jednoduchý (strojový) mechanizmus

In physics, the device capable of making the performance of mechanical work easier by overcoming a force of resistance (the load) at one point by the application of a more convenient force (the effort) at some other point. There are six simple machines:

(1)   lever

(2)   wedge

(3)   inclined plane

(4)   screw

(5)   pulley

(6)   wheel and axle

sliding contact

jazdec (reostatu)

The moving part of the common wire-wound rheostat.

slow neutron

pomalý neutrón

A neutron with a kinetic energy of less 10² eV.

Snell’s law

Snellov zákon

The law of the refraction of light:

n₁.sin α = n₂.sin β,

where n₁ and n₂ are the refractive indices of the two media, α is the angle of incidence, and β is the angle of refraction.

solar day

solárny deň

The interval between two successive returns of the sun to the meridian. The mean solar day of 24 hours is the average value of the solar day for one year.

solar eclipse

zatmenie slnka

Eclipse that occurs when the shadow of the moon falls on the earth.

solar system

slnečná sústava

The name given to the Sun and the bodies held in orbit around it by its gravity, which include planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto), planetary satellites (moons), asteroids, and comets.

solar year

solárny rok, slnečný rok

The average interval between two successive returns of the sun to the first point of Aries; it is 365.242 mean solar days.

solenoid

solenoid, valcová cievka

A coil of wire wound on a cylindrical former in which the length of the former is greater than its diameter.

solid

pevná látka, pevné skupenstvo

A state of matter in which there is a three-dimensional regularity and a substance retains its shape.

solid angle

priestorový uhol

Symbol Ω. The three-dimensional angle formed by the vertex of a cone.

solid-state physics

fyzika pevných látok

The study of the physical properties of solids, in particular their thermal, electrical and magnetic properties.

solution

roztok

A homogeneous mixture of a liquid (the solvent) with a gas or solid (the solute).

sound

zvuk

A longitudinal wave motion in an elastic medium that can be heard by the human ear. The frequency of sounds lies in the range of roughly 20 Hz to 20 kHz.

source

zdroj

In electronic, the electrode from which charge carriers enter the channel in a field effect transistor.

space

1.priestor

2. okolitý vesmír

1. A property of the universe that enables physical phenomena to be extended into three mutually perpendicular directions.

2. (Also called the outer space)

The part of the universe that lies outside the earth’s atmosphere.

space-time

priestoročas

Space and time considered as a single entity, mathematically described by a vector in four dimensions.

space-time continuum

priestoročas, priestoročasové kontinuum

See space-time.

spark

iskra

Short for electric spark.

spark chamber

iskrová komora

A device for detecting charged particles.

special theory of relativity

špeciálna teória relativity

The theory proposed by Einstein in 1905 that refers to inertial frames of reference. It assumes that physical laws are identical in all frames of reference and that the speed of light in vacuum, c, is constant throughout the universe and is independent of the speed of the observer.

specific heat capacity

merná tepelná kapacita

Symbol c. The heat capacity (C) per unit mass (m) of a substance.

c = C/m.

It is measured in J.kg^-1K^-1.

speed

rýchlosť (v zmysle veľkosť rýchlosti)

The ratio of the distance covered by a body to the time taken. Speed is a scalar quantity, i.e. no direction is given. Compare velocity.

speed of light

rýchlosť svetla

Symbol c. The speed at which electromagnetic radiation travels.

The speed of light in a vacuum is

c = 299,792,458 m.s^-1.

speed of sound

rýchlosť zvuku

The speed at which sound waves are propagated through a material medium.

In air at 20˚C sound travels at 344 m.s^-1, in water at 20˚C it travels at 1461 m.s^-1.

spherical polar coordinate system

sférická súradnicová sústava

Coordinate system in three-dimensional space in which a point P is given in coordinates (r,ê,j), where r is distance of P from the origin, ê is the angle between the z-axis and the radius vector OP, and j is the angle between the x-axis and the radius vector OP.

spherical polar coordinates

sférické súradnice

(r,ê,j) - used in three-dimensional systems only.

spin

spin

The part of the total angular momentum of a particle that is distinct from its orbital angular momentum. According to quantum theory, this is quantised and is restricted to whole-number multiples of h/4π, where h is the Planck constant, i.e. spin = Sh/4π, where S=0, ±1, ±2, etc., or if we put s=S/2,

spin = sh/2π,

where s is the spin quantum number. Therefore spin is characterised by a quantum number s. For an electron s = ± ½, implying a spin of +h/4π when it is spinning one direction and -h/4π when it is spinning in the other.

spin quantum number

spinové kvantové číslo

Symbol s (or m_s). The quantum number which gives the spin of the individual electrons and can have the values +½ or -½.

See also atom

square wave

obdĺžnikovité kmity

An electrical signal that switches suddenly and regularly between two values, generally remaining at each of the two values for equal periods of time.

standard model

štandardný model

The combination of quantum chromodynamics to describe strong interactions, electroweak theory to give a unified description of the electromagnetic interaction and the weak interaction, and the general theory of relativity to describe classical gravitational interactions.

standard temperature and pressure (s.t.p.)

normálna teplota a tlak, normálne podmienky

The standard conditions used as a basis for calculations involving quantities that vary with temperature and pressure.

They are 273.15 K (0˚C) and 101.325 Pa.

standing wave

stojaté vlnenie

Same as stationary wave. The term is used mainly in mechanics.

star

hviezda

A self-luminous celestial body that generates nuclear energy within its core.

star cluster

hviezdokopa

A group of stars that are sufficiently close to each other for them to be physically associated.

state of matter

skupenstvo [látky]

One of the three physical states in which matter can exist, i.e. solid, liquid, or gas.

static electricity

statická elektrina

The effects produced by electric charges at rest, including the forces between charged bodies and the field they produce.

stationary wave

stacionárne vlnenie, stacionárna vlna

A form of wave in which the profile of the wave does not move through the medium but remains stationary. This is in contrast to a travelling (or progressive) wave

steady (voltage)

nemenné, stále (napätie)

Stefan constant

Stefanova-Boltzmannova konštanta

Same as Stefan-Boltzmann constant, i. e.

σ = 5.6697 x 10^-8 Js^-1m^-2K^-4.

Stefan’s law

Stefanov-Boltzmannov zákon

Same as Stefan-Boltzmann law.

Stefan-Boltzmann constant

Stefanova-Boltzmannova konštanta

σ = 5.6697 x 10^-8 Js^-1m^-2K^-4.

Stefan-Boltzmann law

Stefanov-Boltzmannov zákon

The total energy radiated per unit surface area of a black body in unit time (M_e) is proportional to the fourth power of its thermodynamic temperature (T), i.e.

M_e = σT⁴,

where σ is the constant of proportionality called the Stefan-Boltzmann constant.

steradian

steradián

Symbol sr. The supplementary SI unit of solid angle. One steradian is the solid angle that encloses a surface on a sphere equal to the square of the radius of the sphere.

straight-line motion

priamočiary pohyb

A motion of a body in which all the points in the body follow parallel straight lines all the time during the motion.

strain

relatívne predĺženie

Symbol ε. A measure of the extent to which a body is deformed when it is subjected to a stress.

Linear strain: ε = (l₁ - l₀)/l₀, where l₁, is the original length and l₁ is the final length.

Bulk strain: ε = (V₁ - V₀)/V₀, where V₁, is the original volume and V₁ is the final volume.

stress

napätie (nie elektrické napätie!)

See tensile stress.

strip

pásik

strong interaction

silná interakcia

One of the four fundamental interactions, some 100 times stronger than the electromagnetic interaction, that functions only between hadrons and is responsible for the force between nucleons that gives the atomic nucleus its great stability. It operates at very short range inside the nucleus (10^-15 m).

subcritical reaction

reakcia vyhasínajúca

Type of a nuclear chain reaction in a nuclear reactor.

superconductivity

supravodivosť

The disappearance of electrical resistance, exhibited by some materials (called superconductors) at low temperatures.

superconductor

supravodič

Any material that exhibits superconductivity.

supercritical reaction

reakcia lavínovite sa zväčšujúca

Type of a nuclear chain reaction in a nuclear reactor.

superfluidity

supratekutosť

The disappearance of all viscosity in liquid helium-4 below 2.2 K.

supernova

supernova

A sudden brightening of a star as the outer layers are blown off when the core collapses to form a neutron star.

supplementary units

doplnkové jednotky

radian (rad) and steradian (sr).

tachyon

tachyon

A hypothetical particle travelling faster than the speed of light.

telescope

ďalekohlad, teleskop

An instrument that collects radiation from a distant object in order to produce an image of it or enable the radiation to be analysed.

television tube

televízna obrazová elektrónka, televízna trubica

A form of cathode-ray tube in which the beam is made to scan the screen 625 times to form a frame, with 25 new frames being produced every second. Each frame creates a picture by variations in the intensity of the beam as it forms each line.

temperature

teplota

Symbol T or t. The property of a body or region of space that determines whether or not there will be a net flow of heat into it or out of it from a neighbouring body or region and in which direction (if any).

It is measured, according to one of the temperature scales, in ˚C, K, or ˚F.

temperature scale

teplotná stupnica

Any of scales to measure temperature characterised by two fixed points and a division of the fundamental interval between these two pints.

The three most used temperature scales are:

(1)   International Practical Temperature Scale, expressed in kelvins (K)

(2)   Celsius scale, expressed in degrees Celsius (˚C)

(3)   Fahrenheit scale, expressed in degrees Fahrenheit (˚F)

temporary magnetism

dočasný magnetizmus

Magnetism in a body that is present when the body is in a magnetic field but that largely disappears when it is removed from the field.

tensile stress

normálové napätie

Symbol σ_n. The force (F) per unit area (S) on a body that tends to cause it to deform.

σ_n = F/S.

termionic emission

termiónová emisia

The emission of electrons, usually into a vacuum, from a heated conductor.

tesla

tesla

Symbol T. The SI unit of magnetic flux density.

thermal conduction

kondukcia, prenos tepla vedením

The transmission of heat through a substance from a region of high temperature to a region of lower temperature by collisions between atoms and molecules (gases and most liquids) or fast-moving electrons and ions (solid and liquid metals).

thermal conductivity

merná tepelná vodivosť

Symbol l.

A measure of the ability of a substance to conduct heat. For a block of material of cross section S, the energy transferred per unit time E/t, between faces a distance, l, apart is given by

E/t = lS(T₂ - T₁)/l,

where T₂ and T₁ are the temperatures of the faces. The SI unit is Js^-1m^-1K^-1.

thermionic valve

elektrónka, termiónová elektrónka

An electronic valve based on thermionic emission.

thermistor

termistor

A semiconductor electronic device designed to exploit the decrease in resistance with increasing temperature.

thermodynamic temperature

termodynamická teplota

Symbol T. Physical quantity that gives temperature of a body or system as positive numbers (and, theoretically, zero), used for scientific purposes. The SI unit of thermodynamic temperature is Kelvin (K).

thermodynamics

termodynamika

The study of the laws that govern the conversion of energy from one form to another, the direction in which heat will flow, and the availability of energy to do work.

threshold (n.)

prah

The minimum value of a parameter or variable that will produce a specified effect.

threshold frequency

hraničná frekvencia

Symbol f₀. The minimal frequency in a photoelectric effect at which the ejection of an electron will occur. It is given by the equation

hf = W_v,

where h is the Planck constant and W_v is the work function.

time

čas

Symbol t. The continuous passage of existence, often defined as a dimension that enables two otherwise identical events that occur at the same point in space to be distinguished.

It is measured in seconds (s).

time dilation

dilatácia času

The effect that results in any moving clock running more slowly than when at rest according to the special theory of relativity.

time-dependent Schrödinger equation

časová Schrödingerova rovnica

iħ.δψ/δt = (-(h²/2m)Δ + U)ψ,

where ψ is the wave function, i the imaginary unit (i² = -1), ħ the rationalised Planck constant, Δ is the Laplace operator, m the particle’s mass, and U its potential energy.

time-independent Schrödinger equation

bezčasová Schrödingerova rovnica

(-(h²/2m)Δ + U)ψ = Eψ,

where h is the Planck constant, Δ is the Laplace operator, m the particle’s mass, E its total energy, and U its potential energy.

torque

moment dvojice síl, točivý moment

The product of a force and its perpendicular distance from a point about which it causes rotation or torsion. It is measured in Nm.

torsion

torzia, stáčanie

A twisting deformation produced by a torque or couple.

total internal reflection

úplný (vnútorný) odraz (svetla)

The total reflection of a beam of light at the interface of one medium and another medium of lower refractive index, when the angle of incidence to the second medium exceeds a specific critical angle.

trajectory

trajektória

A set of all points in space that a moving particle has had during its motion between two specified points.

transformer

transformátor

A device for transferring electrical energy from one alternating current circuit to another with a change in voltage, current, phase, or impedance.

transistor

tranzistor

A three-terminal semiconductor device exhibiting the property of gain, so that a small current or voltage can be used to control a larger current, enabling transistors to be used for amplification and switching.

translation

posuvný pohyb

A motion of a body in which all the points in the body follow parallel paths.

translucent (adj.)

priesvitný

Describing a material through which light (or some other specified form of electromagnetic radiation) can pass, but with the light being scattered, so that an object cannot be seen clearly through the material. Compare opaque; transparent.

transparent (adj.)

priehľadný

Describing a material through which light (or some other specified form of electromagnetic radiation) can pass without scattering, so that an object can be seen through the material. Compare opaque; translucent.

transverse wave

priečne vlnenie

A progressive wave where the disturbances are at right angles to the direction of propagation.

travelling wave (progressive wave)

postupné vlnenie

A wave in which energy is transferred from one place to another by the vibrations.

triode

trióda

A thermionic valve with three electrodes (cathode, anode, and control grid).

triple point

trojný bod

The temperature and pressure at which the vapour, liquid, and solid phases of a substance are in equilibrium.

trough

brázda (vlny), vlnové minimum

A point in the wave where its displacement is the lowest possible.

tunnel diode

tunelová dióda

Same as Esaki diode.

tunnel effect

tunelový jav

An effect, a consequence of quantum mechanics, in which electrons are able to tunnel through a narrow potential barrier that would constitute a forbidden region if the electrons were treated as classical particles.

turbulent flow

turbulentné prúdenie

Irregular motion of a fluid with sudden unpredictable changes in flow direction over time or from one part of the fluid to the next.

ultrahigh frequency (UHF)

ultra-krátke vlny

A radio frequency in the range 3 GHz - 300 MHz.

ultraviolet radiation (UV)

ultrafialové žiarenie

Electromagnetic radiation that has wavelengths between that of violet light and long X-rays, i.e. between 400 nm and 4 nm.

uncertainty principle

princíp neurčitosti

Short for Heisenberg uncertainty principle.

unified-field theory

teória jednotného poľa

A comprehensive theory that would relate the electromagnetic, gravitational, strong, and weak interactions (see fundamental interactions) in one set of equations. So far only two interactions were unified, electromagnetic and weak into the electroweak interactions.

unit

jednotka

A specified measure of a physical quantity, such as length, mass, time, etc., multiples of which are used to express magnitudes of that physical quantity.

unit area

jednotková plocha

An area equal to 1 in the particular system of units (e.g. 1 m² in SI units).

unit cell

základná bunka, elementárna bunka

The smallest group of particles (atoms, ions, or molecules) in a crystal that is repeated in three dimensions in the crystal lattice.

unit surface area

jednotková plocha povrchu

A surface area equal to 1 in the particular system of units (e.g. 1 m² in SI units).

unit vector

jednotkový vektor

A vector with magnitude equal to 1.

unit volume

jednotkový objem

A volume equal to 1 in the particular system of units (e.g. 1 m³ in SI units).

universal constant

univerzálna konštanta

Same as fundamental constant.

universe

vesmír

All the matter, energy, and space that exists.

up

up, up-kvark, u-kvark

A flavour of quark, with charge +2/3 in units of electric charge.

upthrust

vztlaková sila

The upward force on an object immersed (totally or partially) in a fluid.