Davisson-Germer experiment (C.J. Davisson, L.H. Germer; 1927)
An experiment that conclusively confirmed the wave nature ofelectrons;
diffraction patterns were observed by an electron beampenetrating into a
nickel target.
De Broglie wavelength (L. de Broglie; 1924)
The prediction that particles also have wave characteristics,where the
effective wavelength of a particle would be inverselyproportional to its
momentum, where the constant ofproportionality is the Planck constant.
Doppler effect (C.J. Doppler)
Waves emitted by a moving observer will be blueshifted(compressed) if
approaching, redshifted (elongated) if receding.It occurs both in sound as
well as electromagnetic phenomena,although it takes on different forms in
each.
Dulong-Petit law (P. Dulong, A.T. Petit; 1819)
The molar heat capacity is approximately equal to the three timesthe
gas constant.
Einstein-Podolsky-Rosen effect
Consider the following quantum mechanical thought-experiment:Take a particle which is at rest and has spin zero. Itspontaneously decays into two fermions (spin 0.5 particles), whichstream away in opposite directions at high speed. Due to the lawof conservation of spin, we know that one is a spin +0.5 and theother is spin -0.5. Which one is which? According to quantummechanics, neither takes on a definite state until it is observed(the wavefunction is collapsed).
The EPR effect demonstrates that if one of the particles isdetected, and its spin is then measured, then the other particle-- no matter where it is in the Universe -- instantaneously isforced to choose as well and take on the role of the otherparticle. This illustrates that certain kinds of quantuminformation travel instantaneously; not everything is limited bythe speed of light.
However, it can be easily demonstrated that this effect doesnot make
faster-than-light communication possible.
Equivalence principle
The basic postulate of A. Einstein's general theory of relativity,which
posits that an acceleration is fundamentallyindistinguishable from a
gravitational field. In other words, ifyou are in an elevator which is
utterly sealed and protected fromthe outside, so that you cannot "peek
outside," then if you feel aforce (weight), it is fundamentally impossible
for you to saywhether the elevator is present in a gravitational field,
orwhether the elevator has rockets attached to it and isaccelerating
"upward."
The equivalence principle predicts interesting generalrelativistic
effects because not only are the twoindistinguishable to human observers,
but also to the Universe aswell, in a way -- any effect that takes place
when an observer isaccelerating should also take place in a gravitational
field, andvice versa.
Ergosphere
The region around a rotating black hole, between the event horizonand
the static limit, where rotational energy can be extractedfrom the black
hole.
Event horizon
The radius of surrounding a black hole at which a particle wouldneed an
escape velocity of lightspeed to escape; that is, thepoint of no return for
a black hole.
Faraday constant; F (M. Faraday)
The electric charge carried by one mole of electrons (or singly-ionized
ions). It is equal to the product of the Avogadroconstant and the
(absolute value of the) charge on an electron; itis
9.648670.104 C/mol.
Faraday's law (M. Faraday)
The line integral of the electric flux around a closed curve
isproportional to the instantaneous time rate of change of themagnetic flux
through a surface bounded by that closed curve.
Faraday's laws of electrolysis (M. Faraday)
1. The amount of chemical change during electrolysis is proportional to the charge passed.
2. The charge required to deposit or liberate a mass is proportional to the charge of the ion, the mass, and inversely proprtional to the relative ionic mass. The constant of proportionality is the Faraday constant.
Faraday's laws of electromagnetic induction (M. Faraday)
1. An electromotive force is induced in a conductor when the magnetic field surrounding it changes.
2. The magnitude of the electromotive force is proportional to the rate of change of the field.
3. The sense of the induced electromotive force depends on the direction of the rate of the change of the field.
Fermat's principle; principle of least time (P. de Fermat)
The principle, put forth by P. de Fermat, states that the pathtaken by
a ray of light between any two points in a system isalways the path that
takes the least time.
Fermi paradox
E. Fermi's conjecture, simplified with the phrase, "Where arethey?"
questioning that if the Galaxy is filled with intelligentand technological
civilizations, why haven't they come to us yet?There are several possible
answers to this question, but since weonly have the vaguest idea what the
right conditions for life andintelligence in our Galaxy, it and Fermi's
paradox are no morethan speculation.
Gauss' law (K.F. Gauss)
The electric flux through a closed surface is proportional to
thealgebraic sum of electric charges contained within that closedsurface.
Gauss' law for magnetic fields (K.F. Gauss)
The magnetic flux through a closed surface is zero; no magneticcharges
exist.
Grandfather paradox
A paradox proposed to discount time travel and show why itviolates causality. Say that your grandfather builds a timemachine. In the present, you use his time machine to go back intime a few decades to a point before he married his wife (yourgrandmother). You meet him to talk about things, and an argumentensues (presumably he doesn't believe that you're hisgrandson/granddaughter), and you accidentally kill him.
If he died before he met your grandmother and never hadchildren, then
your parents could certainly never have met (one ofthem didn't exist!) and
could never have given birth to you. Inaddition, if he didn't live to
build his time machine, what areyou doing here in the past alive and with a
time machine, if youwere never born and it was never built?
Hall effect
When charged particles flow through a tube which has both anelectric
field and a magnetic field (perpendicular to the electricfield) present in
it, only certain velocities of the chargedparticles are preferred, and will
make it undeviated through thetube; the rest will be deflected into the
sides. This effect isexploited in such devices as the mass spectrometer
and in theThompson experiment. This is called the Hall effect.
Hawking radiation (S.W. Hawking; 1973)
The theory that black holes emit radiation like any other hotbody.
Virtual particle-antiparticle pairs are constantly beingcreated in
supposedly empty space. Every once in a while, onewill be created in the
vicinity of a black hole's event horizon.One of these particles might be
catpured by the black hole,forever trapped, while the other might escape
the black hole'sgravity. The trapped particle, which would have negative
energy(by definition), would reduce the mass of the black hole, and
theparticle which escaped would have positive energy. Thus, from adistant,
one would see the black hole's mass decrease and aparticle escape the
vicinity; it would appear as if the black holewere emitting radiation. The
rate of emission has a negativerelationship with the mass of the black
hole; massive black holesemit radiation relatively slowly, while smaller
black holes emitradiation -- and thus decrease their mass -- more rapidly.
Heisenberg uncertainty principle (W. Heisenberg; 1927)
A principle, central to quantum mechanics, which states that themomentum (mass times velocity) and the position of a particlecannot both be known to infinite accuracy; the more you know aboutone, the lest you know about the other.
It can be illustrated in a fairly clear way as follows: Tosee
something (let's say an electron), we have to fire photons atit, so they
bounce off and come back to us, so we can "see" it.If you choose low-
frequency photons, with a low energy, they donot impart much momentum to
the electron, but they give you a veryfuzzy picture, so you have a higher
uncertainty in position sothat you can have a higher certainty in momentum.
On the otherhand, if you were to fire very high-energy photons (x-rays
orgammas) at the electron, they would give you a very clear pictureof where
the electron is (high certainty in position), but wouldimpart a great deal
of momentum to the electron (higheruncertainty in momentum). In a more
generalized sense, the uncertainty principle tellsus that the act of
observing changes the observed in fundamentalway.
Hooke's law (R. Hooke)
The stress applied to any solid is proportional to the strain
itproduces within the elastic limit for that solid. The constant ofthat
proportionality is the Young modulus of elasticity for thatsubstance.
Hubble constant; H0 (E.P. Hubble; 1925)
The constant which determines the relationship between thedistance to a
galaxy and its velocity of recession due to theexpansion of the Universe.
It is not known to great accuracy, butis believed to lie between 49 and 95
Hubble's law (E.P. Hubble; 1925)
A relationship discovered between distance and radial velocity.The
further away a galaxy is away from is, the faster it isreceding away from
us. The constant of proportionality isHubble's constant, H0. The cause is
interpreted as the expansionof space itself.
Huygens' construction; Huygens' principle (C. Huygens)
The mechanics propagation of a wave of light is equivalent toassuming
that every point on the wavefront acts as point source ofwave emission.
Ideal gas constant; universal molar gas constant; R
The constant that appears in the ideal gas equation. It is equalto
8.314 34.
Ideal gas equation
An equation which sums up the ideal gas laws in one simpleequation. It
states that the product of the pressure and thevolume of a sample of ideal
gas is equal to the product of theamount of gas present, the temperature of
the sample, and theideal gas constant.
Ideal gas laws
Boyle's law. The pressure of an ideal gas is inversely proportional to the volume of the gas at constant temperature.
Charles' law. The volume of an ideal gas is directly proportional to the thermodynamic temperature at constant pressure.
The pressure law. The pressure of an ideal gas is directly
proportional to the thermodynamic temperature at constant volume.
Joule-Thomson effect; Joule-Kelvin effect (J. Joule, W. Thomson)
The change in temperature that occurs when a gas expands into aregion
of lower pressure.
Joule's laws
Joule's first law. The heat produced when an electric current flows through a resistance for a specified time is equal to the square of the current multiplied by the resistivity multiplied by the time.
