Физические законы, переменные, принципы

Физические законы, переменные, принципы

Municipal Liceum № 57

Laws, rules, principles, effects, paradoxes, limits, constants,

experiments, & thought-experiments in physics.

Pupil : Morozov Michael

Togliatti

1998

Ampere's law (A.M. Ampere)

The line integral of the magnetic flux around a closed curve

isproportional to the algebraic sum of electric currents flowingthrough

that closed curve. This was later modified to add a second term when it

wasincorporated into Maxwell's equations.

Anthropic principle

Weak anthropic principle. The conditions necessary for the

development of intelligent life will be met only in certain regions that

are limited in space and time. That is, the region of the Universe in

which we live is not necessarily representative of a purely random set

of initial conditions; only those favorable to intelligent life would

actually develop creatures who wonder what the initial conditions of

the Universe were.

Strong anthropic principle. A more forceful argument that the weak

principle: It states, rather straightforwardly, that if the laws of the

Universe were not conducive to the development of intelligent creatures to

ask about the initial conditions of the Universe, intelligent life would

never have evolved to ask the question in the first place. In other

words, the laws of the Universe are the way they are because if they

weren't, you would not be able to ask such a question.

Arago spot (D.F.J. Arago)

A bright spot that appears in the shadow of a uniform disc beingbacklit

by monochromatic light emanating from a point source.

Archimedes' principle

A body that is submerged in a fluid is buoyed up by a force equalin

magnitude to the weight of the fluid that is displaced, anddirected upward

along a line through the center of gravity of thedisplaced fluid.

Atwood's machine

A weight-and-pulley system devised to measure the acceleration dueto

gravity at Earth's surface by measuring the net acceleration ofa set of

weights of known mass around a frictionless pulley.

Avogadro constant; L; NA (Count A. Avogadro; 1811)

The number of atoms or molecules in a sample of an idea gas whichis at

standard temperature and pressure. It is equal to about 6.022 52.1023 mol-

1.

Avogadro's hypothesis (Count A. Avogadro; 1811)

Equal volumes of all gases at the same temperature and pressurecontain

equal numbers of molecules. It is, in fact, only true forideal gases.

Balmer series (J. Balmer; 1885)

An equation which describes the emission spectrum of hydrogen whenan

electron is jumping to the second orbital; four of the linesare in the

visible spectrum, and the remainder are in theultraviolet.

Baryon decay

The theory, predicted by several grand-unified theories, that aclass of

subatomic particles called baryons (of which the nucleons-- protons and

neutrons -- are members) are not ultimately stablebut indeed decay.

Present theory and experimentation demonstratethat if protons are indeed

unstable, they decay with a halflife ofat least 1034 y.

Bernoulli's equation

An equation which states that an irrotational fluid flowingthrough a

pipe flows at a rate which is inversely proportional tothe cross-sectional

area of the pipe. That is, if the pipeconstricts, the fluid flows faster;

if it widens, the fluid flowsslower.

BCS theory (J. Bardeen, L.N. Cooper, J.R. Schrieffer; 1957)

A theory put forth to explain both superconductivity andsuperfluidity.

It suggests that in the superconducting (orsuperfluid) state electrons form

Cooper pairs, where two electronsact as a single unit. It takes a nonzero

amount of energy tobreak such pairs, and the imperfections in the

superconductingsolid (which would normally lead to resistance) are

incapable ofbreaking the pairs, so no dissipation occurs and there is

noresistance.

Biot-Savart law (J.B. Biot, F. Savart)

A law which describes the contributions to a magnetic field by

anelectric current. It is analogous to Coulomb's law forelectrostatics.

Blackbody radiation

The radiation -- the radiance at particular frequencies all acrossthe

spectrum -- produced by a blackbody -- that is, a perfectradiator (and

absorber) of heat. Physicists had difficultyexplaining it until Planck

introduced his quantum of action.

Bode's law

A mathematical formula which generates, with a fair amount ofaccuracy,

the semimajor axes of the planets in order out from theSun. Write down the

sequence 0, 3, 6, 12, 24, . . . and then add4 to each term. Then divide

each term by 10. This is intended togive you the positions of the planets

measured in astronomicalunits.

Bode's law had no theoretical justification when it was

firstintroduced; it did, however, agree with the soon-to-be-

discoveredplanet Uranus' orbit (19.2 au actual; 19.7 au

predicted).Similarly, it predicted a missing planet betwen Mars and

Jupiter,and shortly thereafter the asteroids were found in very

similarorbits (2.8 au actual for Ceres; 2.8 au predicted). However,

theseries seems to skip over Neptune's orbit.

Bohr magneton (N. Bohr)

The quantum of magnetic moment.

Bohr radius (N. Bohr)

The distance corresponding the mean distance of an electron fromthe

nucleus in the ground state.

Boltzmann constant; k (L. Boltzmann)

A constant which describes the relationship between temperatureand

kinetic energy for molecules in an ideal gas. It is equal to1.

Boyle's law (R. Boyle; 1662); Mariotte's law (E. Mariotte; 1676)

The product of the pressure and the volume of an ideal gas atconstant

temperature is a constant.

Brackett series (Brackett)

The series which describes the emission spectrum of hydrogen whenthe

electron is jumping to the fourth orbital. All of the linesare in the

infrared portion of the spectrum.

Bragg's law (Sir W.L. Bragg; 1912)

When a beam of x-rays strikes a crystal surface in which thelayers of

atoms or ions are regularly separated, the maximumintensity of the

reflected ray occurs when the sine of thecompliment of the angle of

incidence is equal to an integermultiplied by the wavelength of x-rays

divided by twice thedistance between layers of atoms or ions.

Brewster's law (D. Brewster)

The extent of the polarization of light reflected from atransparent

surface is a maximum when the reflected ray is atright angles to the

refracted ray.

Brownian motion (R. Brown; 1827)

The continuous random motion of solid microscopic particles

whensuspended in a fluid medium due to the consequence of

continuousbombardment by atoms and molecules.

Carnot's theorem (S. Carnot)

The theorem which states that no engine operating between

twotemperatures can be more efficient than a reversible engine.

centrifugal pseudoforce

A pseudoforce -- a fictitious force resulting from being in a non-

inertial frame of reference -- that occurs when one is moving inuniform

circular motion. One feels a "force" outward from thecenter of motion.

Chandrasekhar limit (S. Chandrasekhar; 1930)

A limit which mandates that no white dwarf (a collapsed,degenerate

star) can be more massive than about 1.2 solar masses.Anything more massive

must inevitably collapse into a neutronstar.

Charles' law (J.A.C. Charles; c. 1787)

The volume of an ideal gas at constant pressure is proportional tothe

thermodynamic temperature of that gas.

Cherenkov radiation (P.A. Cherenkov)

Radiation emitted by a massive particle which is moving fasterthan

light in the medium through which it is travelling. Noparticle can travel

faster than light in vacuum, but the speed oflight in other media, such as

water, glass, etc., are considerablylower. Cherenkov radiation is the

electromagnetic analogue of thesonic boom, though Cherenkov radiation is a

shockwave set up inthe electromagnetic field.

Complementarity principle (N. Bohr)

The principle that a given system cannot exhibit both wave-likebehavior

and particle-like behavior at the same time. That is,certain experiments

will reveal the wave-like nature of a system,and certain experiments will

reveal the particle-like nature of asystem, but no experiment will reveal

both simultaneously.

Compton effect (A.H. Compton; 1923)

An effect that demonstrates that photons (the quantum ofelectromagnetic

radiation) have momentum. A photon fired at astationary particle, such as

an electron, will impart momentum tothe electron and, since its energy has

been decreased, willexperience a corresponding decrease in frequency.

Coriolis pseudoforce (G. de Coriolis; 1835)

A pseudoforce -- a fictitious force, like the centrifugal "force"--

which arises because the rotation of the Earth varies atdifferent

latitutdes (maximum at the equator, zero at the poles).

correspondence principle.

The principle that when a new, more specialized theory is putforth, it

must reduce to the more general (and usually simpler)theory under normal

circumstances. There are correspondenceprinciples for general relativity

to special relativity andspecial relativity to Newtonian mechanics, but the

most widelyknown correspondence principle (and generally what is meant

whenone says "correspondence principle") is that of quantum mechanicsto

classical mechanics.

Cosmic background radiation; primal glow

The background of radiation mostly in the frequency range 3.1011 to

3.108 Hz discovered in space in 1965. It is believedto be the

cosmologically redshifted radiation released by the BigBang itself.

Presently it has an energy density in empty space ofabout

Cosmological redshift

An effect where light emitted from a distant source appearsredshifted

because of the expansion of space itself. Compare withthe Doppler effect.

Coulomb's law

The primary law for electrostatics, analogous to Newton's law

ofuniversal gravitation. It states that the force between two pointcharges

is proportional to the algebraic product of theirrespective charges as well

as proportional to the inverse squareof the distance between them.

CPT theorem

Curie-Weiss law (P. Curie, P.-E. Weiss)

A more general form of Curie's law, which states that thesusceptibility

of a paramagnetic substance is inverselyproportional to the thermodynamic

temperature of the substanceless the Weiss constant, a characteristic of

that substance.

Curie's law (P. Curie)

The susceptibility of a paramagnetic substance is inverselyproportional

to the thermodynamic temperature of the substance.The constant of

proportionality is called the Curie constant.

Dalton's law of partial pressures (J. Dalton)

The total pressure of a mixture of ideal gases is equal to the sumof

the partial pressures of its components; that is, the sum ofthe pressures

that each component would exert if it were presentalone and occuped the

same volume as the mixture.

Davisson-Germer experiment (C.J. Davisson, L.H. Germer; 1927)

An experiment that conclusively confirmed the wave nature ofelectrons;

diffraction patterns were observed by an electron beampenetrating into a

nickel target.

De Broglie wavelength (L. de Broglie; 1924)

The prediction that particles also have wave characteristics,where the

effective wavelength of a particle would be inverselyproportional to its

momentum, where the constant ofproportionality is the Planck constant.

Doppler effect (C.J. Doppler)

Waves emitted by a moving observer will be blueshifted(compressed) if

approaching, redshifted (elongated) if receding.It occurs both in sound as

well as electromagnetic phenomena,although it takes on different forms in

each.

Dulong-Petit law (P. Dulong, A.T. Petit; 1819)

The molar heat capacity is approximately equal to the three timesthe

gas constant.

Einstein-Podolsky-Rosen effect

Consider the following quantum mechanical thought-experiment:Take a

particle which is at rest and has spin zero. Itspontaneously decays into

two fermions (spin 0.5 particles), whichstream away in opposite directions

at high speed. Due to the lawof conservation of spin, we know that one is

a spin +0.5 and theother is spin -0.5. Which one is which? According to

quantummechanics, neither takes on a definite state until it is

observed(the wavefunction is collapsed).

The EPR effect demonstrates that if one of the particles isdetected,

and its spin is then measured, then the other particle-- no matter where it

is in the Universe -- instantaneously isforced to choose as well and take

on the role of the otherparticle. This illustrates that certain kinds of

quantuminformation travel instantaneously; not everything is limited bythe

speed of light.

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)

1. 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)

1. An electromotive force is induced in a conductor when the magnetic

field surrounding it changes.

2. 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.

Ideal 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

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