| The laws list: D |
The laws list D
Dalton's law to Dulon-Petit law.
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D.
- Dalton's law of
partial pressures (J. Dalton)
- The total pressure of a
mixture of ideal gases is equal to the sum of the partial pressures of its
components; that is, the sum of the pressures that each component would
exert if it were present alone 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 of electrons; diffraction patterns were observed by an
electron beam penetrating 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 inversely proportional to
its momentum, where the constant of proportionality is the
Planck constant.
-
- determinism principle
-
- The principle that if one knows the
state to an infinite accuracy of a system at one point in time, one would be
able to predict the state of that system with infinite accuracy at any other
time, past or future. For example, if one were to know all of the positions
and velocities of all the particles in a closed system, then determinism
would imply that one could then predict the positions and velocities of
those particles at any other time. This principle has been disfavored due to
the advent of quantum mechanics, where probabilities take an important part
in the actions of the subatomic world, and the
uncertainty principle implies that one cannot know both the position and
velocity of a particle to arbitrary precision.
-
- Dirac constant; Planck constant,
modified form; hbar
-
- A sometimes more convenient form of the
Planck constant, defined as
hbar =
h/(2 pi).
- Doppler effect (C.J. Doppler)
-
- Waves emitted by a moving object as received by
an 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.
Compare
cosmological redshift.
-
- Drake equation (F. Drake; 1961)
-
- A method of estimating the number of
intelligent, technological species (i.e., able to communicate with
other species) in existence in our Galaxy.
N = R fp ne fl
fi ft L.
N is the number of species described above
at any given moment in our Galaxy. The parameters it is computed from are as
follows:
- R
- the rate of star formation in our Galaxy (in stars per year);
- fp
- the fraction of stars which have planets;
- ne
- the number of habitable planets per system with planets;
- fl
- the fraction of habitable planets upon which life arises;
- fi
- the fraction of these planets upon which life develops
intelligence;
- ft
- the fraction of these planets where the intelligence develops
into a technological civilization capable of communication; and
- L
- the mean lifetime of such a technological civilization.
Of these quantities, only the first -- R --
is known with anything like any reliability; it is on the order of 10 stars
per year. The others, most notably the fractions, are almost entirely pure
speculation at this point. Calculations made by respectable astronomers
differ by something like ten orders of magnitude in the final estimation of
the number of species out there.
- Dulong-Petit law (P. Dulong, A.T.
Petit; 1819)
-
- The molar heat capacity is approximately
equal to the three times the
ideal gas constant:
C = 3
R.
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