PHYSICS DICTIONARY

  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next>

 

British Thermal Unit(BTU)

It is a standard unit of energy that is used in the United States and sometimes in UK. It represents the amount of thermal energy necessary to raise the temperature of one pound of pure water by one Fahrenheit from the temperature at which water has its greatest density i.e. 39 ^oF. The Btu is a measure in so called English system of units.

1Btu = 1055 Joules, a unit of energy in SI units.

Brittle Substances

Substances which break as soon as the stress is increased beyond elastic limit are called brittle substances.

Bronze

A copper rich copper tin alloy.

Brownian Motion

Irregular, random and zigzag motion of suspended particles in liquid is called Brownian motion.

Bubble Chamber

It was designed by D M Glaser in 1952. It is device used to detect ionizing radiation. The principle underlying this chamber is as follows:

The chamber uses super heated liquid (a liquid that has been heated above its normal boiling point by increasing the pressure over it. When the pressure is suddenly reduced to atmospheric pressure, the liquid remains in unstable super heated state for some time.  If during this interval, an ionizing particle traverses the liquid within few milli seconds after the pressure is released, ions are formed which act as centers for formation of vapor bubbles. The vapor bubbles grow at rapid rate and attain a visible size in a time of order of

10^-100 μsec. 

Bulk Modulus

The ratio of bulk stress to bulk strain within the elastic limit is called bulk modulus or coefficient of volume elasticity.

Bulk Stress

If a body is subjected to the same force normal to all its faces such that there is a change in its volume then normal force per unit area is called bulk stress.

Buoyancy

The property of fluid as per which, a net upward force is exerted on the object by the fluid in which object is immersed partially or completely. 

Buoyant Force

As per Archimedes (a Greek mathematician), a body which is completely or partially immersed in a fluid will experience an upward force called buoyant force, which is equal to weight of fluid displaced by object. The buoyant force is due to difference between the pressure at the bottom of the object pushing up on it, and the pressure at the top pushing down.

Burgers Vector

The magnitude and direction of the lattice distortion associated with a dislocation is expressed in terms of a vector called burger vector.

PHYSICS DICTIONARY

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

<Prev>                   <Next>

Bosons

A group of elementary particles named after well known physicist Satyendranath Bose. They are of two types i) Mass less Bosons created by fields; Photons & Gravitons fall under this category ii) Bosons which are formed in strong interactions; Pions & Kaons fall under this category.

  

Boundary

Anything which separates system and surroundings is called boundary (envelope or wall). The envelope may be imaginary or real; it may be rigid or non-rigid; it may be a conductor of heat (diathermic wall) or a non-conductor of heat (adiabatic wall).

Boyle’s Law

Law as per which at constant temperature, the volume of a given mass of a gas is inversely proportional to its pressure.

Brackett Series

It is the spectrum of wavelengths falling in Infrared region formed due to electron transitions from higher energy states to fourth orbit.  

Bragg Curve

It is plot between residual energy of charged particle passing through matter vs stopping power. Variation of stopping power with respect to residual energy is called as Bragg curve. By residual energy, we mean the instantaneous energy of the particle retained by it as it travels through the material.

Bragg’s Law

Bragg’s law was introduced by Sir W H Bragg and his son  Sir W L Bragg. The law states that when X-rays are incident on crystal lattice with angle of incidence equal to angle of scattering; peaks of scattered intensity are observed (constructive interference) when difference in path length is an integral number of wavelength.

Branching Ratio

Branching ratio is a term that is used to characterize the probability of decay through a mode with respect to all other modes. For instance if a nuclide decays through α and γ modes with branching ratios of 0.8 and 0.2, it would imply that α-particle is emitted in 80% of decays while photons are emitted in 20% of decays.

Brass

A copper rich copper zinc alloy. Alloy consists of Copper and Zinc in variable proportions. 

Brazing

American welding society defines it as metal coalescence above 800^oF. Brazing involves bonding of two surfaces by using molten filler material along with flux to eat through oxide layer.

Breakdown Voltage

It is the minimum voltage which when applied to an insulator loses its insulating property and becomes highly electrically conductive.

Breeder Reactor

Type of nuclear reactor capable of producing fissionable material simultaneously at the expense of burning of fissile material, is called as Breeder reactor. Upon neutron absorption by U-238, it gets converted to Pu-239 which is fissile. The coolant used is liquid metal, usually Sodium as it acts as good heat transfer medium without slowing down of neutrons which is essential for breeding ratio. The reactor core uses high enriched U-235 initiate production of fast neutrons. The core is surrounded by blanket of U-238. Upon neutron absorption by U-238, it gets converted to Pu-239 which is fissile. This makes the chain reaction to sustain for longer periods.      

Breeding

Nuclear process used in breeder reactor as per which non fissionable isotopes yield fissionable isotopes upon capture of fast neutrons.

Bremsstrahlung X-rays

The Bremsstrahlung radiation incident on a suitable target, knock out electrons leading to X-rays from target material called as Bremstrahlung X-rays. 

Bremstrahlung

It is a German word which means braking radiation. Radiation emitted in the form of photons when an energetic electron gets decelerated in the field of atomic nucleus in the matter.  Generally speaking, if a charged particle has energy much greater than its rest energy emits Bremsstrahlung radiation if it encounters resistance while moving through a medium.  

Brewster’s Angle of Incidence

It is the angle of incidence of electromagnetic wave at an interface which yields reflected beam which is totally polarized parallel to the interface and a transmitted beam that is partially polarized perpendicular to it.

                                            or

It is the angle at which incident electromagnetic wave crosses interface between two medium without suffering reflection.

Brewster’s Law

According to this law, the light reflected from a surface is completely polarized if the reflected beam and the beam refracted into material form a right angle. If the incident beam is polarized in plane of incidence there will be no reflection at all. Only if incident beam is polarized normal to plane of incidence, it will get reflected.

Brillouin Zones

Electrons moving in a periodic potential lattice can have energy values only between allowed regions or zones called as Brillouin zones.