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 Maxwell’s equations.
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.
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-
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
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 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
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.
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
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
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
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
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
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
Dulong-Petit law (P. Dulong, A.T. Petit; 1819)
The molar heat capacity is approximately equal to the three timesthe
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.
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
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
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
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.
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
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?
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
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 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
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
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
Lambert’s third law. The luminous intensity of light decreases
exponentially with the distance that it travels through an absorbing
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
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
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
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
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.
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
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 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
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
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
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
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
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.
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
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
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
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
A formula which describes all of the characteristics of
hydrogen’sspectrum, including the Balmer, Lyman, Paschen, Brackett,
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 speeds.
An effect that causes atomic energy levels to be split becauseelectrons
have intrinsic angular momentum (spin) in addition totheir extrinsic
orbital angular momentum.
The distance from a rotating black hole where no observer canpossibly
remain at rest (with respect to the distant stars)because of inertial frame
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.
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
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
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.
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
Rules governing the formation of products during certain types
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.
«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
4.10-14 J m3.
5.6697.10-8 W m2.K4.