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 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.
Pfund series
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 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
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 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.
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.
