Реферат: Физические законы, переменные, принципы
Municipal Liceum № 57
Laws, rules, principles, effects, paradoxes, limits, constants, experiments,
& thought-experiments in physics.
Pupil : Morozov Michael
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
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
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.
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.
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 52.10
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.
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.
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.
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.
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
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
Carnot's theorem (S. Carnot)
The theorem which states that no engine operating between twotemperatures can
be more efficient than a reversible engine.
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
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).
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 3.10
11 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
An effect where light emitted from a distant source appearsredshifted because
of the expansion of space itself. Compare withthe Doppler effect.
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.
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
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
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
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
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
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.
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.
The region around a rotating black hole, between the event horizonand the
static limit, where rotational energy can be extractedfrom the black hole.
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
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
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
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.
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?
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
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
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
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
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
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
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
Lambert's third law. The luminous intensity of light decreases
exponentially with the distance that it travels through an absorbing medium.
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
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
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.
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.
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
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
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.
Pressure applied to an enclosed imcompressible static fluid istransmitted
undiminished to all parts of the fluid.
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
permittivity of free space; electric constant; e0
The ratio of the electric displacement to the intensity of theelectric field
producing it in vacuum. It is equal to 8.854.10-12 F/m.
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.
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
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
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 point in time, one would be able to predict thestate of that system with
infinite accuracy at any other time,past or future. For example, if one were
to know all of thepositions and velocities of all the particles in a closed
system,then determinism would imply that one could then predict thepositions
and velocities of those particles at any other time.This principle has been
disfavored due to the advent of quantummechanics, where probabilities take an
important part in theactions of the subatomic world, and the Heisenberg
uncertaintyprinciple implies that one cannot know both the position andvelocity
of a particle to arbitrary precision.
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
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.
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
An effect that causes atomic energy levels to be split becauseelectrons have
intrinsic angular momentum (spin) in addition totheir extrinsic orbital angular
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
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.
The phenomena by which, at sufficiently low temperatures, aconductor can
conduct charge with zero resistance.
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.
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
point of view (and from everyone else on Earth),Albert seems to speed off for a
long time, linger around, and thenreturn. Thus he should be the younger one,
which is what we see.But from Albert's point of view, it's Henrik (and the
whole of the 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 point here is thatthe symmetry
was broken. Albert did something that Henrik didnot -- Albert accelerated in
turning around. Henrik did noaccelerating, as he and all the other people on
the Earth canattest to (neglecting gravity). So Albert broke the symmetry,
andwhen he returns, he is the younger one.
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.
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.
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.
Rules governing the formation of products during certain types oforganic
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
1. «Basic Postulats» by Gabrele O’Hara
2. «Elementary Physic For Students» by Bill Strong
3. «Atomic Physic» by Steve Grevesone
4. «Optica» by Steve Grevesone
5. «Thermodynamic’s Laws» by Kay Fedos