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
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

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.

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
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

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 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 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.

The most commonly seen are the laws of conservation of mass-energy

(formerly two conservation laws before A. Einstein), ofelectric charge, of

linear momentum, and of angular momentum.There are several others that deal

more with particle physics,such as conservation of baryon number, of

strangeness, etc., whichare conserved in some fundamental interactions but

not others.

Law of reflection

For a wavefront intersecting a reflecting surface, the angle

ofincidence is equal to the angle of reflection.

Laws of black hole dynamics

First law of black hole dynamics. For interactions between black holes

and normal matter, the conservation laws of total energy, total momentum,

angular momentum, and electric charge, hold.

Second law of black hole dynamics. With black hole interactions, or

interactions between black holes and normal matter, the sum of the surface

areas of all black holes involved can never decrease.

Laws of thermodynamics

First law of thermodynamics. The change in internal energy of a system

is the sum of the heat transferred to or from the system and the work done

on or by the system.

Second law of thermodynamics. The entropy — a measure of the

unavailability of a system’s energy to do useful work — of a closed system

tends to increase with time.

Third law of thermodynamics. For changes involving only perfect

crystalline solids at absolute zero, the change of the total entropy is

zero.

Zeroth law of thermodynamics. If two bodies are each in thermal

equilibrium with a third body, then all three bodies are in thermal

equilibrium with each other.

Lawson criterion (J.D. Lawson)

A condition for the release of energy from a thermonuclearreactor. It

is usually stated as the minimum value for theproduct of the density of the

fuel particles and the containmenttime for energy breakeven. For a half-

and-half mixture ofdeuterium and tritium at ignition temperature, nG t is

between1014 and 1015 s/cm3.

Le Chatelier’s principle (H. Le Chatelier; 1888)

If a system is in equilibrium, then any change imposed on thesystem

tends to shift the equilibrium to reduce the effect of thatapplied change.

Lenz’s law (H.F. Lenz; 1835)

An induced electric current always flows in such a direction thatit

opposes the change producing it.

Loschmidt constant; Loschmidt number; NL

The number of particles per unit volume of an ideal gas atstandard

temperature and pressure. It has the value 2.68719.1025 m-3.

Lumeniferous aether

A substance, which filled all the empty spaces between matter,which was

used to explain what medium light was «waving» in. Nowit has been

discredited, as Maxwell’s equations imply thatelectromagnetic radiation can

propagate in a vacuum, since theyare disturbances in the electromagnetic

field rather thantraditional waves in some substance, such as water waves.

Lyman series

The series which describes the emission spectrum of hydrogen

whenelectrons are jumping to the ground state. All of the lines arein the

ultraviolet.

Mach’s principle (E. Mach; 1870s)

The inertia of any particular particle or particles of matter

isattributable to the interaction between that piece of matter andthe rest

of the Universe. Thus, a body in isolation would have noinertia.

Magnus effect

A rotating cylinder in a moving fluid drags some of the fluidaround

with it, in its direction of rotation. This increases thespeed in that

region, and thus the pressure is lower.Consequently, there is a net force

on the cylinder in thatdirection, perpendicular to the flow of the fluid.

This is calledthe Magnus effect.

Malus’s law (E.L. Malus)

The light intensity travelling through a polarizer is proportionalto

the initial intensity of the light and the square of the cosineof the angle

between the polarization of the light ray and thepolarization axis of the

polarizer.

Maxwell’s demon (J.C. Maxwell)

A thought experiment illustrating the concepts of entropy. Wehave a

container of gas which is partitioned into two equal sides;each side is in

thermal equilibrium with the other. The walls(and the partition) of the

container are a perfect insulator. Now imagine there is a very small

demon who is waiting at thepartition next to a small trap door. He can

open and close thedoor with negligible work. Let’s say he opens the door

to allow afast-moving molecule to travel from the left side to the right,

orfor a slow-moving molecule to travel from the right side to the left, and

keeps it closed for all other molecules. The net effectwould be a flow of

heat — from the left side to the right — eventhough the container was in

thermal equilibrium. This is clearlya violation of the second law of

thermodynamics. So where did we go wrong? It turns out that information

hasto do with entropy as well. In order to sort out the moleculesaccording

to speeds, the demon would be having to keep a memory ofthem — and it

turns out that increase in entropy of the simplemaintenance of this simple

memory would more than make up for thedecrease in entropy due to the heat

flow.

Maxwell’s equations (J.C. Maxwell; 1864)

Four elegant equations which describe classical electromagnetismin all

its splendor. They are:

Gauss’ law. The electric flux through a closed surface is proportional

to the algebraic sum of electric charges contained within that closed

surface.

Gauss’ law for magnetic fields. The magnetic flux through a closed

surface is zero; no magnetic charges exist.

Faraday’s law. The line integral of the electric flux around a closed

curve is proportional to the instantaneous time rate of change of the

magnetic flux through a surface bounded by that closed curve.

Ampere’s law, modified form. The line integral of the magnetic flux

around a closed curve is proportional to the sum of two terms: first, the

algebraic sum of electric currents flowing through that closed curve; and

second, the instantaneous time rate of change of the electric flux through

a surface bounded by that closed curve.

In addition to describing electromagnetism, his equations alsopredict

that waves can propagate through the electromagneticfield, and would always

propagate at the same speed — these are electromagnetic waves.

Meissner effect (W. Meissner; 1933)

The decrease of the magnetic flux within a superconducting metalwhen it

is cooled below the critical temperature. That is,superconducting

materials reflect magnetic fields.

Michelson-Morley experiment (A.A. Michelson, E.W. Morley; 1887)

Possibly the most famous null-experiment of all time, designed toverify

the existence of the proposed «lumeniferous aether» throughwhich light

waves were thought to propagate. Since the Earthmoves through this aether,

a lightbeam fired in the Earth’sdirection of motion would lag behind one

fired sideways, where noaether effect would be present. This difference

could be detectedwith the use of an interferometer.

The experiment showed absolutely no aether shift whatsoever,where one

should have been quite detectable. Thus the aetherconcept was discredited

as was the constancy of the speed oflight.

Millikan oil drop experiment (R.A. Millikan)

A famous experiment designed to measure the electronic charge.Drops of

oil were carried past a uniform electric field betweencharged plates.

After charging the drop with x-rays, he adjustedthe electric field between

the plates so that the oil drop wasexactly balanced against the force of

gravity. Then the charge onthe drop would be known. Millikan did this

repeatedly and foundthat all the charges he measured came in integer

multiples only ofa certain smallest value, which is the charge on the

electron.

Newton’s law of universal gravitation (Sir I. Newton)

Two bodies attract each other with equal and opposite forces;

themagnitude of this force is proportional to the product of the twomasses

and is also proportional to the inverse square of thedistance between the

centers of mass of the two bodies.

Newton’s laws of motion (Sir I. Newton)

Newton’s first law of motion. A body continues in its state of rest or

of uniform motion unless it is acted upon by an external force.

Newton’s second law of motion. For an unbalanced force acting on a

body, the acceleration produces is proportional to the force impressed; the

constant of proportionality is the inertial mass of the body.

Newton’s third law of motion. In a system where no external forces are

present, every action is always opposed by an equal and opposite reaction.

Ohm’s law (G. Ohm; 1827)

The ratio of the potential difference between the ends of aconductor to

the current flowing through it is constant; theconstant of proportionality

is called the resistance, and isdifferent for different materials.

Olbers’ paradox (H. Olbers; 1826)

If the Universe is infinite, uniform, and unchanging then theentire sky

at night would be bright — about as bright as the Sun.The further you

looked out into space, the more stars there wouldbe, and thus in any

direction in which you looked your line-of-sight would eventually impinge

upon a star. The paradox isresolved by the Big Bang theory, which puts

forth that theUniverse is not infinite, non-uniform, and changing.

Pascal’s principle

Pressure applied to an enclosed imcompressible static fluid

istransmitted undiminished to all parts of the fluid.

Paschen series

The series which describes the emission spectrum of hydrogen whenthe

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

infrared portion of the spectrum.

Pauli exclusion principle (W. Pauli; 1925)

No two identical fermions in a system, such as electrons in anatom, can

have an identical set of quantum numbers.

Peltier effect (J.C.A. Peltier; 1834)

The change in temperature produced at a junction between twodissimilar

metals or semiconductors when an electric currentpasses through the

junction.

permeability of free space; magnetic constant; m 0

The ratio of the magnetic flux density in a substance to theexternal

field strength for vacuum. It is equal to 4 p . 10-7 H/m.

permittivity of free space; electric constant; e0

The series which describes the emission spectrum of hydrogen whenthe

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

infrared portion of the spectrum.

Photoelectric effect

An effect explained by A. Einstein that demonstrate that lightseems to

be made up of particles, or photons. Light can exciteelectrons (called

photoelectrons) to be ejected from a metal.Light with a frequency below a

certain threshold, at anyintensity, will not cause any photoelectrons to be

emitted fromthe metal. Above that frequency, photoelectrons are emitted

inproportion to the intensity of incident light. The reason is that a

photon has energy in proportion to itswavelength, and the constant of

proportionality is Planck’sconstant. Below a certain frequency — and thus

below a certainenergy — the incident photons do not have enough energy to

knockthe photoelectrons out of the metal. Above that threshold

energy,called the workfunction, photons will knock the photoelectrons outof

the metal, in proportion to the number of photons (theintensity of the

light). At higher frequencies and energies, thephotoelectrons ejected

obtain a kinetic energy corresponding tothe difference between the photon’s

energy and the workfunction.

Planck constant; h

The fundamental constant equal to the ratio of the energy of aquantum

of energy to its frequency. It is the quantum of action.It has the value

6.626196.10-34 J.s.

Planck’s radiation law

A law which more accurately described blackbody radiation becauseit

assumed that electromagnetic radiation is quantized.

Poisson spot (S.D. Poisson)

See Arago spot. Poisson predicted the existence of such a spot,and

actually used it to demonstrate that the wave theory of lightmust be in

error.

Principle of causality

The principle that cause must always preceed effect. Moreformally, if

an event A («the cause») somehow influences an eventB («the effect») which

occurs later in time, then event B cannotin turn have an influence on event

A. The principle is best illustrated with an example. Say thatevent A

constitutes a murderer making the decision to kill hisvictim, and that

event B is the murderer actually committing theact. The principle of

causality puts forth that the act ofmurder cannot have an influence on the

murderer’s decision tocommit it. If the murderer were to somehow see

himself committingthe act and change his mind, then a murder would have

beencommitted in the future without a prior cause (he changed hismind).

This represents a causality violation. Both time traveland faster-than-

light travel both imply violations of causality,which is why most

physicists think they are impossible, or atleast impossible in the general

sense.

Principle of determinism

The principle that if one knows the state to an infinite accuracyof a

system at one
Rayleigh criterion; resolving power

A criterion for the how finely a set of optics may be able

todistinguish. It begins with the assumption that central ring ofone image

should fall on the first dark ring of the other.relativity principle;

principle of relativity

Rydberg formula

A formula which describes all of the characteristics of

hydrogen’sspectrum, including the Balmer, Lyman, Paschen, Brackett,

andPfund series.

Schroedinger’s cat (E. Schroedinger; 1935)

A thought experiment designed to illustrate the counterintuitiveand

strange notions of reality that come along with quantummechanics.

A cat is sealed inside a closed box; the cat has ample air,food, and

water to survive an extended period. This box isdesigned so that no

information (i.e., sight, sound, etc.) canpass into or out of the box —

the cat is totally cut off fromyour observations. Also inside the box with

the poor kitty(apparently Schroedinger was not too fond of felines) is a

phialof a gaseous poison, and an automatic hammer to break it, floodingthe

box and killing the cat. The hammer is hooked up to a Geigercounter; this

counter is monitoring a radioactive sample and isdesigned to trigger the

hammer — killing the cat — should aradioactive decay be detected. The

sample is chosen so thatafter, say, one hour, there stands a fifty-fifty

chance of a decayoccurring.

The question is, what is the state of the cat after that onehour has

elapsed? The intuitive answer is that the cat is eitheralive or dead, but

you don’t know which until you look. But it is one of them. Quantum

mechanics, on the other hands, saysthat the wavefunction describing the cat

is in a superposition ofstates: the cat is, in fact, fifty per cent alive

and fifty percent dead; it is both. Not until one looks and «collapses

thewavefunction» is the Universe forced to choose either a live cator a

dead cat and not something in between.

This indicates that observation also seems to be an importantpart of

the scientific process — quite a departure from theabsolutely objective,

deterministic way things used to be withNewton.

Schwarzchild radius

The radius that a spherical mass must be compressed to in order

totransform it into a black hole; that is, the radius of compressionwhere

the escape velocity at the surface would reach lightspeed.

Snell’s law; law of refraction

A relation which relates the change in incidence angle of awavefront

due to refraction between two different media.

Speed of light in vacuo

One of the postulates of A. Einstein’s special theory ofrelativity,

which puts forth that the speed of light in vacuum —often written c, and

which has the value 299 792 458 m/s — ismeasured as the same speed to all

observers, regardless of theirrelative motion. That is, if I’m travelling

at 0.9 c away fromyou, and fire a beam of light in that direction, both you

and Iwill independently measure the speed of that beam as c. One of the

results of this postulate (one of the predictionsof special relativity is

that no massive particle can beaccelerated to (or beyond) lightspeed, and

thus the speed of lightalso represents the ultimate cosmic speed limit.

Only masslessparticles (photons, gravitons, and possibly neutrinos, should

theyindeed prove to be massless) travel at lightspeed, and all

otherparticles must travel at slower speeds.

Spin-orbit effect

An effect that causes atomic energy levels to be split becauseelectrons

have intrinsic angular momentum (spin) in addition totheir extrinsic

orbital angular momentum.

Static limit

The distance from a rotating black hole where no observer canpossibly

remain at rest (with respect to the distant stars)because of inertial frame

dragging.

Stefan-Boltzmann constant; sigma (Stefan, L. Boltzmann)

The constant of proportionality present in the Stefan-Boltzmannlaw. It

is equal to

Stefan-Boltzmann law (Stefan, L. Boltzmann)

The radiated power (rate of emission of electromagnetic energy) ofa hot

body is proportional to the emissivity, an efficiencyrating, the radiating

surface area, and the fourth power of thethermodynamic temperature. The

constant of proportionality is theStefan-Boltzmann constant.

Stern-Gerlach experiment (O. Stern, W. Gerlach; 1922)

An experiment that demonstrates the features of spin (intrinsicangular

momentum) as a distinct entity apart from orbital angularmomentum.

Superconductivity

The phenomena by which, at sufficiently low temperatures, aconductor

can conduct charge with zero resistance.

Superfluidity

The phenomena by which, at sufficiently low temperatures, a fluidcan

flow with zero viscosity.

Superposition principle of forces

The net force on a body is equal to the sum of the forcesimpressed upon

it.

Superposition principle of states

The resultant quantum mechnical wavefunction due to two or

moreindividual wavefunctions is the sum of the individualwavefunctions.

Superposition principle of waves

The resultant wave function due to two or more individual wavefunctions

is the sum of the individual wave functions.

Thomson experiment; Kelvin effect (Sir W. Thomson [later Lord Kelvin])

When an electric current flows through a conductor whose ends

aremaintained at different temperatures, heat is released at a

rateapproximately proportional to the product of the current and

thetemperature gradient.

Twin paradox

One of the most famous «paradoxes» in history, predicted by

A.Einstein’s special theory of relativity. Take two twins, born onthe same

date on Earth. One, Albert, leaves home for a triparound the Universe at

very high speeds (very close to that oflight), while the other, Henrik,

stays at home at rests. Specialrelativity predicts that when Albert

returns, he will find himselfmuch younger than Henrik. That is actually

not the paradox. The paradox stems fromattempting to naively analyze the

situation to figure out why.From Henrik’s
Earth) that are travelling, not he. According to specialrelativity, if

Henrik is moving relative to Albert, then Albertshould measure his clock as

ticking slower — and thus Henrik isthe one who should be younger. But

this is not what happens.

So what’s wrong with our analysis? The key Ultraviolet catastrophe

A shortcoming of the Rayleigh-Jeans formula, which attempted todescribe

the radiancy of a blackbody at various frequencies of theelectromagnetic

spectrum. It was clearly wrong because as thefrequency increased, the

radiancy increased without bound;something quite not observed; this was

dubbed the «ultravioletcatastrophe.» It was later reconciled and explained

by theintroduction of Planck’s radiation law.

Universal constant of gravitation; G

The constant of proportionality in Newton’s law of universalgravitation

and which plays an analogous role in A. Einstein’sgeneral relativity. It

is equal to 6.664.10-11 N.m2/kg2.

Van der Waals force (J.D. van der Waals)

Forces responsible for the non-ideal behavior of gases, and forthe

lattice energy of molecular crystals. There are three causes:dipole-dipole

interaction; dipole-induced dipole moments; anddispersion forces arising

because of small instantaneous dipolesin atoms.

Wave-particle duality

The principle of quantum mechanics which implies that light

(and,indeed, all other subatomic particles) sometimes act like a wave,and

sometime act like a particle, depending on the experiment youare

performing. For instance, low frequency electromagneticradiation tends to

act more like a wave than a particle; highfrequency electromagnetic

radiation tends to act more like aparticle than a wave.

Widenmann-Franz law

The ratio of the thermal conductivity of any pure metal to

itselectrical conductivity is approximately constant for any

giventemperature. This law holds fairly well except at lowtemperatures.

Wien’s displacement law

For a blackbody, the product of the wavelength corresponding tothe

maximum radiancy and the thermodynamic temperature is aconstant. As a

result, as the temperature rises, the maximum ofthe radiant energy shifts

toward the shorter wavelength (higherfrequency and energy) end of the

spectrum.

Woodward-Hoffmann rules

Rules governing the formation of products during certain types

oforganic reactions.

Young’s experiment; double-slit experiment (T. Young; 1801)

A famous experiment which shows the wave nature of light (andindeed of

other particles). Light is passed from a small sourceonto an opaque screen

with two thin slits. The light is refractedthrough these slits and

develops an interference pattern on theother side of the screen.

Zeeman effect; Zeeman line splitting (P. Zeeman; 1896)

The splitting of the lines in a spectrum when the source is exposed to

a magnetic field.

Used Literature.

«Basic Postulats» by Gabrele O’Hara

«Elementary Physic For Students» by Bill Strong

«Atomic Physic» by Steve Grevesone

«Optica» by Steve Grevesone

«Thermodynamic’s Laws» by Kay Fedos

————————

380 622 . 10-23 J

K.

4.10-14 J m3.

Km .

s.Mpc

J .

K.mol

5.6697.10-8 W m2.K4.