Dictionary of Physics by Frantisek Fecko: J

J/y (J/psi)	J/y-mezón	A meson containing the charmed quark and antiquark. Discovered independently by two experimental groups in 1974, it was the first evidence for the existence of charm.
jet propulsion	tryskový pohon	The propulsion of a body by means of a force produced by discharging a fluid in the form of a jet.
joule	joule	Symbol J. The SI unit of work and energy.
Joule heat	Joulovo teplo	The heat produced in a conductor as a result of the passage of an electric current through the conductor. The quantity of heat produced is given by Joule’s law.
Joule’s laws	Joulove zákony	1. The heat (Q) produced when an electric current (I) flows through a resistance (R) for a time (t) is given by Q = I²Rt. 2. The internal energy of a given mass of an ideal gas is independent of its volume and pressure, being a function of temperature alone.
junction detector	detektor s polovodičovou vrstvou	A sensitive detector of ionising radiation in which the output is a current pulse proportional to the energy falling in or near the depletion region of a reverse-biased semiconductor junction.
junction transistor	plošný tranzistor, tranzistor, bipolárny tranzistor	A semiconductor device that exhibits the important property of gain - a small current can be used to control a much larger one. The commonest type of junction transistor is the NPN transistor. It consists of a thin layer of lightly doped p-type semiconductor, called the base, sandwiched between two more heavily doped pieces of n-type semiconductor material, the collector and the emitter.
kaon	kaon, K-mezón	A K-meson. See meson.
K-capture	elektrónový K-záchyt	A type of nuclear capture in which the nucleus of an atom absorbs an electron from the innermost orbit (the K shell) to transform into a different nucleus. In this process the atom is left in an excited state and generally decays by emission of an X-ray photon.
kelvin	Kelvin	Symbol K. The SI unit of thermodynamic temperature. One kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
Kepler’s laws	Keplerove zákony	Three laws of planetary motion formulated by Johannes Kepler. (1) The orbits of the planets are elliptical with the sun at one focus of the ellipse. (2) Each planet revolves around the sun so that an imaginary line (the radius vector) connecting the planet to the sun sweeps out equal areas in equal times. (3) The ratio of the square of each planet’s sidereal period to the cube of its distance from the sun is a constant for all the planets.
kilogram	kilogram	Symbol kg. The SI unit of mass. One kilogram is a mass equal to that of the international platinum-iridium prototype kept by the International Bureau of Weights and Measures at Sèvres, near Paris.
kinematic equation	kinematická rovnica	See equation of motion.
kinematics	kinematika	The branch of mechanics concerned with the motions of objects without being concerned with the forces that cause the motion.
kinetic energy	kinetická energia	Symbol E_k. The energy of movement. The kinetic energy of a mass (m) moving at a speed (v) is E_k = ½mv².
kinetic theory	kinetická teória	A theory that explains the physical properties of matter in terms of the motions of its constituent particles (atoms and molecules). The theory is largely the work of Count Rumford, James Joule, and James Clark Maxwell.
Kirchhoff’s laws	Kirchhoffove zákony	Two laws relating toelectric circuits, first formulated by G.R.Kirchhoff. 1. (the current law): The algebraic sum of the currents flowing through all the wires in a network that meet at a point is zero. SI_k = 0 A, or SI_in = SI_out 2. (the voltage law): The algebraic sum of the e.m.f.s within any closed circuit is equal to the sum of the products of the currents and the resistances in the various portions of the circuit. SU_ei = SR_kI_k
klystron	klystron	An electron tube that generates or amplifies microwaves by velocity modulation.
labelling	značkovanie	The process of replacing a stable atom in a compound with a radioisotope of the same element to enable its path through a biological or mechanical system to be traced by the radiation it emits.
lag	oneskorenie, oneskorovanie, časový posun	The time delay between a specified maximum value of one wave or vibration and the maximum value of another wave or vibration.
Lagrangian	Lagrangián, /lagranži(j)a:n/, Lagrangeova funkcia	Symbol L. A function used to define a dynamical system in terms of functions of coordinates, velocities, and times given by: L = T - U, where T is the kinetic energy of the system and U is the potential energy of the system.
Lamb shift	Lambov posun	A small energy difference between two levels (²S½ and ²P½) in the hydrogen spectrum. The shift results from the quantum interaction between the atomic electron and the electromagnetic radiation.
lambda point	bod lambda	Symbol l. The temperature of 2.186 K below which helium-4 becomes a superfluid.
laminar flow	laminárne prúdenie	Smooth flow of a fluid in which the fluid moves in layers without fluctuations or turbulence so that successive particles passing the same point have the same velocity.
lanthanides	lantanoidy	All elements with atomic numbers between 90 and 103 of periodic table beginning with Thorium and ending with Lawrencium.
Laplace operator	Laplaceov operátor	Symbol Δ or ². Δ = . = δ²/δx² + δ²/δy² + δ²/δz².
laser	laser	Acronym for light amplification by stimulated emission of radiation. A device for producing an intense parallel beam of coherent light.
latent heat	latentné teplo	Symbol L. The quantity of heat absorbed or released when a substance changes its physical phase at constant temperature.
latitude	(zemepisná) šírka	A measure of position on the surface of the Earth, or any other planet. Latitude is measured in degrees north or south of the equator. See also longitude.
lattice	(kryštálová) mriežka	The regular arrangement of atoms, ions, or molecules in a crystalline solid. See crystal lattice.
lattice energy	energia mriežky	A measure of the stability of a crystal lattice, given by the energy that would be released per mole if atoms, ions, or molecules of the crystal were brought together from infinite distances apart to form the lattice.
law of the reflection	zákon odrazu	(1) The incident ray, the reflected ray, and the normal to the reflecting interface at the point of the incidence are all in the same plane. (2) The angle of incidence equals the angle of reflection.
law of the refraction	zákon lomu	Same as Snell’s law.
lead	olovo
length	dĺžka
lens	šošovka	A curved, ground, and polished piece of glass, moulded plastic, or other transparent material used for the refraction of light.
Lenz’s law	Lenzov zákon	An induced electric current always flows in such a direction that it opposes the change producing it.
lepton	lepton	Any of a class of elementary particles not affected by the strong nuclear force. Three charged leptons are known, the electron, the muon and the tau lepton. For each of these particles there is also a neutrino, a light (probably massless) particle carrying no charge, but the same quantum number as the charged lepton.
lever	páka	One of the six simple machines.
liberated	uvoľnená	e.g. energy liberated
liberation of energy	uvoľnenie energie
lift (n.)	vztlak (v aerodynamike)
light (n.)	svetlo	The form of electromagnetic radiation to which the human eye is sensitive and on which our visual awareness of the universe and its contents relies (see colour).
light year	svetelný rok	The distance travelled by light in a vacuum during one year. 1 LY = 9.465 x 10¹⁵ m.
light-emitting diode (LED)	svetlo-emitujúca dióda, dióda emitujúca svetlo (hovorovo ledka)	A semiconductor device that converts electrical energy into visible light or infrared light. It comprises a diode in which the energy loss for charge carriers crossing the depletion layer is large enough for them to produce a photon of light.
lightning	blesk	A high-energy luminous electrical discharge that passes (a) between a charged cloud and a point on the surface of the earth, (b) between two charged clouds, or (c) between oppositely charged layers of the same cloud.
line defect	čiarová porucha	Same as dislocation.
line spectrum	čiarové spektrum	An emission spectrum or absorption spectrum in which the wavelengths absorbed or emitted form a number of separate very narrow ranges of lines.
linear accelerator (linac)	lineárny urýchľovač	A type of particle accelerator in which charged particles are accelerated in a straight line.
lines of force	siločiary	Imaginary lines in a field of force that enable the direction and strength of the field to be visualised.
liquid	kvapalina	A phase of matter between that of a crystalline solid and a gas.
liquid crystal	kvapalný kryštál, tekutý kryštál	A substance that flows like a liquid but has some order in its arrangement of molecules.
Lissajous figures	Lissajousove obrazce	A curve in one plane traced by a point moving under the influence of two independent harmonic motions, perpendicular to each other.
load	záťaž	1. (in electricity and electronics): Any device to which electrical power is supplied. 2. (in mechanics): An object on which work is done by some machine, or the force acting on that object.
locus	množina bodov (určená rovnicou/rovnicami)	A set of points whose location is specified by an equation, forming a continuous line.
logic circuit	logický obvod	An electronic system handling digital signals and containing one or more logic gates.
logic gate	logické hradlo, hradlo	The basic building block of any digital electronic system. A logic gate gives an output that is high or low depending on the state of one or more inputs.
long wave	dlhé vlny	Radio waves with a wavelength longer than about 600 m.
longitude	(zemepisná) dĺžka	A measure of position on the surface of the Earth, or any other planet. Longitude is measured in degrees east or west of the prime meridian, i.e. a line running from pole to pole and passing through a specified point. On Earth, the prime meridian is fixed as passing through Greenwich in the UK. See also latitude.
longitudinal wave	pozdĺžne vlnenie	A progressive wave in which the motion of the particles that make up the wave is to-and-fro along the direction in which the wave is travelling. Compare transverse wave.
Lorentz transformations	Lorentzove transformácie	A set of equations for transforming the position and motion parameters from a frame of reference with origin at O and coordinates (x,y,z) to a frame moving relative to it with origin at O’ and coordinates at (x’,y’,z’). They are: x’ = β(x - vt) y’ = y z’ = z t’ = β(t - vx/c²), where v is the relative velocity of separation of o and O’, c is the speed of light, and β = (1 - v²/c²)^-½.
loudness	hlasitosť (zvuku)	The physiological perception of sound intensity.
low frequency (LF)	nízka frekvencia	A radio frequency in the range 30 kHz - 300 kHz.
lumen	lumen	Symbol lm. The SI unit of luminous flux.
luminescence	luminiscencia	The emission of light by a substance for any reason other than a rise in temperature.
luminosity	žiarivý výkon hviezdy	Symbol L. The brightness of a star defined as the total energy radiated in unit time. L = 4πr²Φ_e/S, where Φ_e is the radiant flux falling perpendicular on the surface area S in the distance r from a star. Assuming that the radiation of a star is as that of a black body, i.e. Φ_e = σT_ef⁴/4πr², where T_ef is the effective temperature (the temperature of a black body having the same radius as the star and radiating the same amount of energy per unit area in one second), the luminosity is L = SσT_ef⁴, where σ is the Stefan-Boltzmann constant.
luminous flux	svetelný tok	Symbol Φ. A measure of the rate of flow of light, i.e. the radiant flux in the wavelength range 380-760 nm, corrected for the dependence on wavelength of the sensitivity of the human eye. It is measured in lumens (lm).
luminous intensity	svietivosť	Symbol I. A measure of the light-emitting ability of a light source, either generally or in a particular direction. It is measured in candelas (cd).
lunar eclipse	zatmenie mesiaca	An eclipse that occurs when the sun, earth, and moon are in a straight line and the shadow of the earth falls on the moon.
lux	lux	Symbol lx. The SI unit of illuminance.
Mach number	Machovo číslo	The ratio of the relative speeds of a fluid and a rigid body to the speed of sound in that fluid under the same conditions of temperature and pressure. If the Mach number exceeds 1 the fluid or body is moving at a supersonic speed. If the Mach number exceeds 5 it is said to be hypersonic.
machine	(strojový) mechanizmus, (mechanické) zariadenie	A device capable of making the performance of mechanical work easier, usually 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. In physics, the six so-called simple machines are the lever, wedge, inclined plane, screw, pulley, and wheel-and-axle.
magic numbers	magické čísla	Numbers of neutrons or protons that occur in atomic nuclei to produce very stable structures. The magic for both protons and neutrons numbers are 2, 8, 20, 28, 50, and 82. For neutrons 126 and 184 are also magic numbers and for protons 114 is a magic number.
magnet	magnet	A piece of magnetic material that has been magnetised and is therefore surrounded by a magnetic field.
magnetic constant	magnetická konštanta, (zastaralo: permeabilita vákua)	m₀ = 4p x 10^-7 H.m^-1
magnetic field	magnetické pole	A field of force that exists around a magnetic body or a current-carrying conductor. The strength and direction of the field can be given in terms of the magnetic flux density (or magnetic induction), symbol B; it can also be given in terms of the magnetic field strength (or magnetic intensity), symbol H. Numerically, H = B/μ, where μ is the permeability of the medium.
magnetic field lines	magnetické indukčné čiary	Lines that show the direction of a magnetic field at each point.
magnetic field strength	intenzita magnetického poľa	Symbol H. H = B/μ, where μ is the permeability of the medium. It is measured in A.m^-1.
magnetic flux	magnetický indukčný tok	Symbol f. A measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. The flux Φ through an area S at the angle α with B is given by Φ = \|B\|.S.cos a The SI unit of magnetic flux is the weber (Wb).
magnetic flux density	magnetická indukcia	Symbol B. The magnetic flux per unit area of a magnetic field at right angles to the magnetic force, i.e. \|B\| = dΦ/dS. It can be defined in terms of the effects the field has, for example by B = F/qvsin α, where F is the force a moving charge q would experience if it was travelling at a velocity v in a direction making an angle α with that of the field. The SI unit is the tesla.
magnetic force	magnetická sila	The attractive or repulsive force exerted on a magnetic pole or a moving electric charge in a a magnetic field.
magnetic induction	magnetická indukcia	Same as magnetic flux density.
magnetic intensity	intenzita magnetického poľa	Same as magnetic field strength.
magnetic moment	magnetický moment	Symbol m. The strength of field produced at large distances from a loop carrying a current (I) and enclosing an area (S): m = IS. The SI unit is Am².
magnetic quantum number	magnetické kvantové číslo	Symbol m. The quantum number which governs the energies of electrons in an external magnetic field. This can take values of +l, +(l-1), … , 1, 0, -1, … , -(l-1), -l. In an s-subshell (i.e. l = 0) the value of m = 0. In a p-subshell (l = 1), m can have values +1, 0, -1; i.e. there are three p-orbitals in the p-subshell, usually designated p_x, p_y, and p_z. See also atom
magnetism	magnetizmus	A group of phenomena associated with magnetic fields.
magneton	magneton	A unit for measuring magnetic moments of nuclear, atomic, or molecular magnets. The Bohr magneton μ_B has the value of the classical magnetic moment of an electron, given by μ_B = 9.274 x 10^-24 Am². The nuclear magneton μ_N is obtained by replacing the mass of the electron by the mass of the proton and is therefore given by μ_N = 5.05 x 10^-27 Am².
magnitude	1. veľkosť (vektora) 2. magnitúda (astron.)	1. A positive real number (or number 0 if it is a zero vector) expressing the length of a vector. 2. A measure of the brightness of a star. See apparent magnitude; absolute magnitude.
majority carrier	majoritný nosič	The type of charge carrier that predominates in a particular region or material in a semiconductor.
maser	maser	Acronym for microwave amplification by stimulated emission of radiation. A device for amplifying or generating microwaves by means of stimulated emission.
mass	hmotnosť	Symbol m. A measure of a body’s inertia, i.e. its resistance to acceleration. According to Newton’s laws of motion, if two unequal masses, m₁ and m₂, are allowed to collide, in the absence of any other forces both will experience the same force of collision. If the two bodies acquire accelerations a₁ and a₂ as a result of the collision, then m₁a₁ = m₂a₂. This equation enables two masses to be compared. If one of the masses is regarded as a standard of mass, the mass of all other masses can be measured in terms of this standard. The body used for this purpose is a 1-kg cylinder of platinum-iridium alloy, called the international standard of mass. Mass defined in this way is called the inertial mass of the body (m_i). Mass can also be defined in terms of the gravitational force it produces. m_g = Fd²/MG, where M is the mass of a standard body situated a distance d from the body of mass m_g, F is the gravitational force between them and G is the gravitational constant. The mass defined in this way is called the gravitational mass of the body (m_g). In the 19th century Roland Eotvos showed experimentally that gravitational mass and inertial mass are indistinguishable, i.e. m_i= m_g.
matter	hmota, látka	The collective term for all atoms. Matter is any substance with mass and which is not antimatter. In particle physics, matter is defined as all substances with a positive baryon or lepton number.
Maxwell’s equations	Maxwellove rovnice	A set of differential equations describing the space and time dependence of the electromagnetic field and forming the basis of classical electrodynamics. In SI units the equations are: (a) vacuum: (1) rot B = μ₀j + μ₀ε₀.δE/δt (2) rot E = -δB/δt (3) div B = 0 (4) div E = ρ/ε₀ (b) material medium: (1) rot H = j + δD/δt (2) rot E = -δB/δt (3) div B = 0 (4) div D = ρ where D = εE is the electric displacement, B = μH is the magnetic flux density, H is the magnetic field strength, E is the electric field strength ρ is the volume charge density. j is the electric current density.
Maxwell-Boltzmann distribution	Maxwellovo-Boltzmannovo rozdelenie	A law describing the distribution of speeds among the molecules of a gas.
mean (adj.)	stredný, priemerný
mean distance	stredná vzdialenosť
mean solar day	stredný solárny deň	The average value of the solar day for one year. It is equal to 24 hours.
mechanics	mechanika	The study of the interactions between matter and the forces acting on it.
medium (pl. media)	prostredie
melting point	teplota topenia	The temperature at which a solid changes into a liquid.
mental model	myšlienkový model
meson	mezón	Any of a family of unstable hadrons, made up of a quark and an antiquark. They exist as positive, negative and neutral particles and they include kaon, the pi-meson and the psi-particle.
metre	meter	Symbol m. The SI unit of length. One meter is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 second.
microscope	mikroskop	A device for forming a magnified image of a small object.
microwave background radiation	reliktové kozmické žiarenie	Electromagnetic radiation in the frequency range 3 x 10¹¹ Hz to 3 x 10⁸ Hz, received from all directions in space with a spectrum characteristic of a black body at a temperature of 2.7 K.
microwaves	mikrovlny	Electromagnetic waves with wavelengths in the range 10^-3 m to 0.03 m.
Milky Way	Mliečna Cesta	Our galaxy, i.e. the galaxy comprising our solar system (including the Sun).
minority carrier	minoritný nosič, menšinový nosič	The type of charge carrier with the lower concentration (as opposed to majority carrier) in a semiconductor.
mirage	fatamorgána	An optical phenomenon that occurs as a result of the bending of light rays through layers of air having very large temperature gradients.
mirror	zrkadlo	A surface that reflects most of the light falling on it.
missing mass	chýbajúca hmota	The mass of the mater in the universe that cannot be observed by direct observations of its emitted or absorbed electromagnetic radiation.
mixture	zmes	A substance containing two or more elements or compounds, but where there is no chemical bonding between the constituents of the mixture.
moderator	moderátor	A substance that slows down free neutrons in a nuclear reactor.
modulation	modulácia	The process of superimposing the characteristics of a periodic signal onto a carrier wave so that the information contained in the signal can be transmitted by the carrier wave. The commonest types are amplitude modulation (AM), frequency modulation (FM) and phase modulation.
modulus of elasticity	modul pružnosti	See elastic modulus.
mole	mol	Symbol mol. The SI unit of amount of substance. One mole is the amount of substance that contains as many elementary units (atoms, molecules, ions, radicals, electrons) as there are atoms in 0.012 kg of carbon-12.
molecule	molekula	The smallest part of a chemical compound that can take part in a chemical reaction.
moment	moment	Short for moment of a force.
moment of a force	moment sily	Symbol M. A measure of the turning effect produced by a force about an axis. M = r x F where r is the position vector of the point of application of the force F.
moment of inertia	moment zotrvačnosti	Symbol I. The moment of inertia of a massive body about an axis is the sum of all the products formed by multiplying the magnitude of each element of mass (mi) by the square of its distance (r) from the line, i.e. I = Σm_ir_i².
momentum	hybnosť	Symbol p. The product of a mass (m) of a body and its velocity (v), i.e. p = mv.
monochromatic radiation	monochromatické žiarenie	Electromagnetic radiation, especially visible radiation, of only one frequency or wavelength.
moon	mesiac
motion (mechanical motion)	mechanický pohyb	A change in the position of a body or system with respect to time, as measured by a particular observer in a particular frame of reference.
muon	mión	Symbol μ⁺ and μ^-. A charged lepton with a mass about 210 times that of the electron, to which it decays with a half-life of about 2 x 10^-6s.
mutual induction	vzájomná indukcia	Symbol M. A measure of the effect whereby a changing current in one coil will induce an e.m.f. in another coil. It is equal to the induced e.m.f. (U_i) divided by the rate of change of current (dI/dt). If two coils have a mutual inductance M, a rate of change of current dI/dt in one will produce an e.m.f. in the other of U_i = M.dI/dt The SI unit of mutual inductance is the henry.