 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 grandunified 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 ~10^{34} 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, 18521908)

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.
 BiotSavart 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 = (mu_{0} I)/(4 pi r^{2}) 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
currentproducing 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.
 blackhole dynamic laws; laws of blackhole dynamics

 first law of black hole dynamics

For interactions between black
holes and normal matter, the conservation laws of
massenergy, electric charge, linear momentum, and angular momentum,
hold. This is analogous to the first law of thermodynamics.
 second law of black hole dynamics

With blackhole 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, TitiusBode 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 soontobediscovered
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.
 bradyon

See tardon.
 Bragg's law (Sir W.L. Bragg; 1912)

When a beam of xrays 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 xrays,
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.

The laws list
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Laws, rules, principles, effects, paradoxes, limits, constants, experiments, & thoughtexperiments in physics.

