PHYSICS (732351), страница 2
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However, it can be easily demonstrated that this effect doesnot make faster-than-light communication possible.
Equivalence principle
The basic postulate of A. Einstein's general theory of relativity,which posits that an acceleration is fundamentallyindistinguishable from a gravitational field. In other words, ifyou are in an elevator which is utterly sealed and protected fromthe outside, so that you cannot "peek outside," then if you feel aforce (weight), it is fundamentally impossible for you to saywhether the elevator is present in a gravitational field, orwhether the elevator has rockets attached to it and isaccelerating "upward."
The equivalence principle predicts interesting generalrelativistic effects because not only are the twoindistinguishable to human observers, but also to the Universe aswell, in a way -- any effect that takes place when an observer isaccelerating should also take place in a gravitational field, andvice versa.
Ergosphere
The region around a rotating black hole, between the event horizonand the static limit, where rotational energy can be extractedfrom the black hole.
Event horizon
The radius of surrounding a black hole at which a particle wouldneed an escape velocity of lightspeed to escape; that is, thepoint of no return for a black hole.
Faraday constant; F (M. Faraday)
The electric charge carried by one mole of electrons (or singly-ionized ions). It is equal to the product of the Avogadroconstant and the (absolute value of the) charge on an electron; itis
9.648670.104 C/mol.
Faraday's law (M. Faraday)
The line integral of the electric flux around a closed curve isproportional to the instantaneous time rate of change of themagnetic flux through a surface bounded by that closed curve.
Faraday's laws of electrolysis (M. Faraday)
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The amount of chemical change during electrolysis is proportional to the charge passed.
2. The charge required to deposit or liberate a mass is proportional to the charge of the ion, the mass, and inversely proprtional to the relative ionic mass. The constant of proportionality is the Faraday constant.
Faraday's laws of electromagnetic induction (M. Faraday)
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An electromotive force is induced in a conductor when the magnetic field surrounding it changes.
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The magnitude of the electromotive force is proportional to the rate of change of the field.
3. The sense of the induced electromotive force depends on the direction of the rate of the change of the field.
Fermat's principle; principle of least time (P. de Fermat)
The principle, put forth by P. de Fermat, states that the pathtaken by a ray of light between any two points in a system isalways the path that takes the least time.
Fermi paradox
E. Fermi's conjecture, simplified with the phrase, "Where arethey?" questioning that if the Galaxy is filled with intelligentand technological civilizations, why haven't they come to us yet?There are several possible answers to this question, but since weonly have the vaguest idea what the right conditions for life andintelligence in our Galaxy, it and Fermi's paradox are no morethan speculation.
Gauss' law (K.F. Gauss)
The electric flux through a closed surface is proportional to thealgebraic sum of electric charges contained within that closedsurface.
Gauss' law for magnetic fields (K.F. Gauss)
The magnetic flux through a closed surface is zero; no magneticcharges exist.
Grandfather paradox
A paradox proposed to discount time travel and show why itviolates causality. Say that your grandfather builds a timemachine. In the present, you use his time machine to go back intime a few decades to a point before he married his wife (yourgrandmother). You meet him to talk about things, and an argumentensues (presumably he doesn't believe that you're hisgrandson/granddaughter), and you accidentally kill him.
If he died before he met your grandmother and never hadchildren, then your parents could certainly never have met (one ofthem didn't exist!) and could never have given birth to you. Inaddition, if he didn't live to build his time machine, what areyou doing here in the past alive and with a time machine, if youwere never born and it was never built?
Hall effect
When charged particles flow through a tube which has both anelectric field and a magnetic field (perpendicular to the electricfield) present in it, only certain velocities of the chargedparticles are preferred, and will make it undeviated through thetube; the rest will be deflected into the sides. This effect isexploited in such devices as the mass spectrometer and in theThompson experiment. This is called the Hall effect.
Hawking radiation (S.W. Hawking; 1973)
The theory that black holes emit radiation like any other hotbody. Virtual particle-antiparticle pairs are constantly beingcreated in supposedly empty space. Every once in a while, onewill be created in the vicinity of a black hole's event horizon.One of these particles might be catpured by the black hole,forever trapped, while the other might escape the black hole'sgravity. The trapped particle, which would have negative energy(by definition), would reduce the mass of the black hole, and theparticle which escaped would have positive energy. Thus, from adistant, one would see the black hole's mass decrease and aparticle escape the vicinity; it would appear as if the black holewere emitting radiation. The rate of emission has a negativerelationship with the mass of the black hole; massive black holesemit radiation relatively slowly, while smaller black holes emitradiation -- and thus decrease their mass -- more rapidly.
Heisenberg uncertainty principle (W. Heisenberg; 1927)
A principle, central to quantum mechanics, which states that themomentum (mass times velocity) and the position of a particlecannot both be known to infinite accuracy; the more you know aboutone, the lest you know about the other.
It can be illustrated in a fairly clear way as follows: Tosee something (let's say an electron), we have to fire photons atit, so they bounce off and come back to us, so we can "see" it.If you choose low-frequency photons, with a low energy, they donot impart much momentum to the electron, but they give you a veryfuzzy picture, so you have a higher uncertainty in position sothat you can have a higher certainty in momentum. On the otherhand, if you were to fire very high-energy photons (x-rays orgammas) at the electron, they would give you a very clear pictureof where the electron is (high certainty in position), but wouldimpart a great deal of momentum to the electron (higheruncertainty in momentum). In a more generalized sense, the uncertainty principle tellsus that the act of observing changes the observed in fundamentalway.
Hooke's law (R. Hooke)
The stress applied to any solid is proportional to the strain itproduces within the elastic limit for that solid. The constant ofthat proportionality is the Young modulus of elasticity for thatsubstance.
Hubble constant; H0 (E.P. Hubble; 1925)
The constant which determines the relationship between thedistance to a galaxy and its velocity of recession due to theexpansion of the Universe. It is not known to great accuracy, butis believed to lie between 49 and 95
Hubble's law (E.P. Hubble; 1925)
A relationship discovered between distance and radial velocity.The further away a galaxy is away from is, the faster it isreceding away from us. The constant of proportionality isHubble's constant, H0. The cause is interpreted as the expansionof space itself.
Huygens' construction; Huygens' principle (C. Huygens)
The mechanics propagation of a wave of light is equivalent toassuming that every point on the wavefront acts as point source ofwave emission.
I
deal gas constant; universal molar gas constant; R
The constant that appears in the ideal gas equation. It is equalto 8.314 34.
Ideal gas equation
An equation which sums up the ideal gas laws in one simpleequation. It states that the product of the pressure and thevolume of a sample of ideal gas is equal to the product of theamount of gas present, the temperature of the sample, and theideal gas constant.
Ideal gas laws
Boyle's law. The pressure of an ideal gas is inversely proportional to the volume of the gas at constant temperature.
Charles' law. The volume of an ideal gas is directly proportional to the thermodynamic temperature at constant pressure.
The pressure law. The pressure of an ideal gas is directly proportional to the thermodynamic temperature at constant volume.
Joule-Thomson effect; Joule-Kelvin effect (J. Joule, W. Thomson)
The change in temperature that occurs when a gas expands into aregion of lower pressure.
Joule's laws
Joule's first law. The heat produced when an electric current flows through a resistance for a specified time is equal to the square of the current multiplied by the resistivity multiplied by the time.
Joule's second law. The internal energy of an ideal gas is independent of its volume and pressure, depending only on its temperature.
Josephson effects (B.D. Josephson; 1962)
Electrical effects observed when two superconducting materials areseparated by a thin layer of insulating material.
Kepler's laws (J. Kepler)
Kepler's first law. A planet orbits the Sun in an ellipse with the Sun at one focus.
Kepler's second law. A ray directed from the Sun to a planet sweeps out equal areas in equal times.
Kepler's third law. The square of the period of a planet's orbit is proportional to the cube of that planet's semimajor axis; the constant of proportionality is the same for all planets.
Kerr effect (J. Kerr; 1875)
The ability of certain substances to differently refract lightwaves whose vibrations are in different directions when thesubstance is placed in an electric field.
Kirchhoff's law of radiation (G.R. Kirchhoff)
The emissivity of a body is equal to its absorptance at the sametemperature.
Kirchhoff's rules (G.R. Kirchhoff)
The loop rule. The sum of the potential differences encountered in a round trip around any closed loop in a circuit is zero.
The point rule. The sum of the currents toward a branch point is equal to the sum of the currents away from the same branch point.
Kohlrausch's law (F. Kohlrausch)
If a salt is dissolved in water, the conductivity of the solutionis the sum of two values -- one depending on the positive ions andthe other on the negative ions.
Lambert's laws (J.H. Lambert)
Lambert's first law. The illuminance on a surface illuminated by light falling on it perpendicularly from a point source is proportional to the inverse square of the distance between the surface and the source.
Lambert's second law. If the rays meet the surface at an angle, then the illuminance is also proportional to the cosine of the angle with the normal.
Lambert's third law. The luminous intensity of light decreases exponentially with the distance that it travels through an absorbing medium.
Landauer's principle
A principle which states that it doesn't explicitly take energy tocompute data, but rather it takes energy to erase any data,since erasure is an important step in computation.
Laplace's equation (P. Laplace)
For steady-state heat conduction in one dimension, the temperaturedistribution is the solution to Laplace's equation, which statesthat the second derivative of temperature with respect todisplacement is zero.
Laue pattern (M. von Laue)
The pattern produced on a photographic film when high-frequencyelectromagnetic waves (such as x-rays) are fired at a crystallinesolid.
Laws of conservation
A law which states that, in a closed system, the total quantity ofsomething will not increase or decrease, but remain exactly thesame. For physical quantities, it states that something canneither be created nor destroyed.
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