The laws list
Balmer series to Brownian motion.

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Balmer series (J. Balmer; 1885)
An equation which describes the emission spectrum of hydrogen when an electron is jumping to the second orbital; four of the lines are in the visible spectrum, and the remainder are in the ultraviolet.
baryon decay
The idea, predicted by several grand-unified theories, that a class of subatomic particles called baryons (of which the nucleons -- protons and neutrons -- are members) are not ultimately stable but indeed decay. Present theory and experimentation demonstrate that if protons are in fact unstable, they decay with a halflife of at least ~1034 y.
beauty criterion (Dirac)
The idea that the more aesthetically pleasing a theory is, the better it is. Naturally this criterion does not stand up to the real test -- whether or not predictions of a given theory agree with observational tests -- but considering that it is a purely aesthetic quality that is being tested, many of the most successful theories (special relativity, general relativity, quantum electrodynamics, etc.) match the criterion particularly well.
becquerel; Bq (after A.H. Becquerel, 1852-1908)
The derived SI unit of activity, defined as the activity of a radionuclide decaying at a rate, on the average, of one nuclear transition every 1 s; it thus has units of s-1.
Bernoulli's equation
In an irrotational fluid, the sum of the static pressure, the weight of the fluid per unit mass times the height, and half the density times the velocity squared is constant throughout the fluid.
Bell's inequality (J.S. Bell; 1964)
A quantum mechanical theorem which demonstrates that if quantum mechanics were to rely on hidden variables, it must have nonlocal properties.
BCS theory (J. Bardeen, L.N. Cooper, J.R. Schrieffer; 1957)
A theory put forth to explain both superconductivity and superfluidity. It suggests that in the superconducting (or superfluid) state electrons form Cooper pairs, where two electrons act as a single unit. It takes a nonzero amount of energy to break such pairs, and the imperfections in the superconducting solid (which would normally lead to resistance) are incapable of breaking the pairs, so no dissipation occurs and there is no resistance.
Biot-Savart law (J.B. Biot, F. Savart)
A law which describes the contributions to a magnetic field by an electric current. It is analogous to Coulomb's law. Mathematically, it is
dB = (mu0 I)/(4 pi r2) dl cross e
where dl is the infinitesimal directed length of the electric current causing the magnetic field, I is the current running through that directed length, r is the distance from that directed length, and e is the unit vector directed from the test point to current-producing length.
blackbody radiation
The radiation -- the radiance at particular frequencies all across the spectrum -- produced by a blackbody -- that is, a perfect radiator (and absorber) of heat. Physicists had difficulty explaining it until Planck introduced his quantum of action.
black-hole dynamic laws; laws of black-hole dynamics
first law of black hole dynamics
For interactions between black holes and normal matter, the conservation laws of mass-energy, electric charge, linear momentum, and angular momentum, hold. This is analogous to the first law of thermodynamics.
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. This is analogous to the second law of thermodynamics, with the surface areas of the black holes being a measure of the entropy of the system.
Bode's law, Titius-Bode law
A mathematical formula which generates, with a fair amount of accuracy, the semimajor axes of the planets in order out from the Sun. Write down the sequence
0, 3, 6, 12, 24, ...
and add 4 to each term:
4, 7, 10, 16, 28, ...
Then divide each term by 10. This leaves you with the series
0.4, 0.7, 1.0, 1.6, 2.8, ...
which is intended to give you the semimajor axes of the planets measured in astronomical units.

Bode's law had no theoretical justification when it was first introduced; it did, however, agree with the soon-to-be-discovered planet Uranus' orbit (19.2 au actual; 19.7 au predicted). Similarly, it predicted a missing planet between Mars and Jupiter, and shortly thereafter the asteroids were found in very similar orbits (2.77 au actual for Ceres; 2.8 au predicted). The series, however, seems to skip over Neptune's orbit. The form of Bode's law (that is, a roughly geometric series) is not surprising, considering our theories on the formation of solar systems, but its particular formulation is thought of as coincidental.

Bohr magneton (N. Bohr)
The quantum of magnetic moment.
Bohr radius (N. Bohr)
The distance corresponding the mean distance of an electron from the nucleus in the ground state of the hydrogen atom.
Boltzmann constant; k (L. Boltzmann)
A constant which describes the relationship between temperature and kinetic energy for molecules in an ideal gas. It is equal to 1.380 622 x 10-23 J/K.
Boyle's law (R. Boyle; 1662); Mariotte's law (E. Mariotte; 1676)
The product of the pressure and the volume of an ideal gas at constant temperature is a constant.

See ideal gas laws.

Brackett series (Brackett)
The series which describes the emission spectrum of hydrogen when the electron is jumping to the fourth orbital. All of the lines are in the infrared portion of the spectrum.
See tardon.
Bragg's law (Sir W.L. Bragg; 1912)
When a beam of x-rays strikes a crystal surface in which the layers of atoms or ions are regularly separated, the maximum intensity of the reflected ray occurs when the complement of the angle of incidence, theta, the wavelength of the x-rays, lambda, and the distance betwen layers of atoms or ions, d, are related by the equation
2 d sin theta = n lambda,
where n is an integer.
Brewster's law (D. Brewster)
The extent of the polarization of light reflected from a transparent surface is a maximum when the reflected ray is at right angles to the refracted ray.
Brownian motion (R. Brown; 1827)
The continuous random motion of solid microscopic particles when suspended in a fluid medium due to the consequence of ongoing bombardment by atoms and molecules.
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