Barns: Unit is used for nuclear scattering interactions. It is used to represent the measure of probability of interaction between small particles. The value of one barn is 10-28m2 and is approximately crossectional area of Uranium nucleus.    


Boyles law:

At a constant temperature, the volume of a given mass of a gas is inversely proportional to its pressure.



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. 


Black body:

A body which completely absorbs radiation of all wavelengths incident on its surface and doesn’t reflect any part of it is called as black body.


It is a body which emits thermal radiations of all wavelengths when heated to high temperature.


Bernoullis principle:

The total energy per unit volume of an incompressible, non-viscous fluid in laminar flow is constant at every point. 


Brownian motion:

Irregular, random and zig-zag motion of suspended particles in liquid is called Brownian motion.


Bose Einstein Condensation:

Phenomenon of rapid increase in number of particles in ground state at temperatures below critical temperature.


Bulk Stress:

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


Balmer series:

The spectrum of wavelength falling in visible region due to transition of electrons from higher orbits to second orbit is called Balmer series.


Binding energy:

The energy equivalent of mass defect is called binding energy. It is this energy which binds nucleons together.


Brackett series:

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


Boiling point:

The temperature at which a liquid starts changing its phase into vapor. 



Instrument invented by Evangelista Toricelli to measure atmospheric pressure. 


Beats: When two sounding bodies of nearly the same frequency and amplitude are sounded together, the resultant sound consists of alternate maxima and minima. This phenomenon in which waxing and Vaning of sound at regular intervals is heard is called beats. The number of beats heard per second is equal to difference in frequency between two sounding bodies.     



Radiation emitted in form of photons when an energetic electron gets influenced by atomic number in the matter. The electron due to deceleration emits dissipated energy in the form of photons called as Bremstrahlung radiation.    


Beta particle:


Black body: Body which absorbs radiations of all wavelengths incident on it. It neither reflects nor transmits any radiation.



Device used to detect thermal radiation which works on principle of change of resistance with temperature.


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.


It is the angle at which incident EM 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 be reflected.


Binding energy:

Energy required for breaking a nucleus into free neutrons and protons.



It is unit for measuring intensity of sound. Whenever intensity of sound increases by a factor of 10, the increase in intensity is said to be 1 bel.



It is an isotope of Boron having an abundance of 19.9% in natural Boron i.e. 11B. The isotope has good cross-section for interaction with thermal neutron and value is about 3837± 9 barns.



Process in which materials meant for vacuum application are subjected to heat condition to reduce out-gassing rate.



American welding society defines it as metal coalescence above

800 F. Brazing involves bonding of two surfaces by using molten filler material along with flux to eat through oxide layer.


Bonding energy:

Energy required for separating two atoms to an infinite distance.



Body centered cubic:

Crystal structure having cubic unit cell with atoms located at all eight corners and a single atom at cubic center.


Burgers vector:

A vector that denotes the magnitude and direction of lattice distortion associated with a dislocation.