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
Atom
Bomb
Nuclear weapon
which harnesses the forces that hold the nucleus of an atom together, by using
the energy released when the nucleus splits into nucleons. The atom bomb works
on principle of nuclear fission. Nuclear reactions occur when neutrons are
fired at closely packed atoms with heavy fissile nuclei like uranium-235 / Plutonium
isotopes. This leads to nuclear fission which further converts to chain
reaction.
Atom
Percent (at %)
It is defined as
concentration specification on basis of number of moles (or atoms) of a
particular element relative to the total number of moles (or atoms) of all elements
within an alloy.
Atom
It is tiny basic
unit of matter which is neutral and from which any substance gets constructed.
It has positively charged nucleus constituting nucleons (Protons &
Neutrons) surrounded by electrons revolving round the nucleus.
Atomic
Clock
It is accurate
type of time device in the world, which is controlled by vibrations of an
atomic or molecular system such as Cesium or Ammonia. The precision of an
atomic clock depends on fact that an atom, caused to oscillate, will always vibrate
at same frequency. NIST-F1, the United States standard atomic clock, is said to
be so accurate that it would neither gain nor lose a second in over 30 yrs.
They are used as primary standard in global navigation satellite system such as
GPS.
Atomic
Mass Unit (amu)
It is defined as
1/12 of mass of Carbon-12 atom. It is average of Proton & Neutron rest mass
i.e. 1.67377 x 10-24 gm. The unit is used to express relative masses
of various isotopes of element.
Atomic
Number
The number of
protons found inside the nucleus of a particular atom. The modern periodic
table is structured based on this number.
Atomic
Orbital
A quantum state
attributed to electron around atom in quantum mechanics to describe wave
characteristic of electron. It is
expressed by mathematical function which is used to calculate probability of
finding any electron in any specific region around atom’s nucleus.
Atomic
Packing Fraction
It is the ratio
of volume of atoms per unit cell to volume of unit cell in a crystal structure.
Atomic
Physics
It is study of structure of atom,
arrangement of electrons around nucleus i.e. energy states, interaction of
atoms with other particles and with electric and magnetic fields.
Atomic
Radius
It is defined as
half the distance between neighboring atoms in a crystal of a pure element.
Atomic
Structure
It is study of
configuration of atom which is essential for knowing many phenomenon involving
electrons. Bohr’s atomic model is early model which has explained structure of
atom to a great extent. Later the limitations of that model overcome by
attributing dual nature to particle. The atomic structure represents the manner
in which electron states are occupied.
Atomic
Weight
It is the
weighted average of the atomic masses of an atom’s naturally occurring isotopes.
It is usually expressed in amu.
Atomicity
Total no. of
atoms present in one molecule of an element of a substance is called as
atomicity.
Atto
Prefix in metric
system denoting a factor of 10-18.
Audio
Frequency
It is the
frequency range of periodic vibrations audible to human ear. The range is 20Hz
to 20 KHz.
Audio
Meter
It is an
instrument for measuring hearing activity for pure tones of normally audible
frequencies.
Aufbau’s
Principle
Principle which
states that sub-shell of lower energy in an atom is filled up first while that
of higher energy is filled up later.
Auger
Effect
See Auger
electron.
Auger
Electron
In photoelectric
effect, following expulsion of photoelectron, another electron from high energy
state may occupy its location emitting X-ray photon. This photon may in turn
eject electron from loosely bound outer electron shell, called auger electron
and such photoelectric effect is called “Auger Effect”.
Aurora
It is a luminous
atmospheric phenomenon appearing as streamers or bands of light sometimes
visible in the night sky in northern or southern regions of the earth. It is
thought to be caused by charged particles from the sun entering the earth’s
magnetic field and stimulating molecules in atmosphere.
