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
Acceptor
Terminology used
in semiconductor physics which refers to the doping atom of group-III element
of periodic table which are deficient of electrons and hence leads to holes
when doped appropriately. The semiconductor having holes as majority charge
carriers is called P-Type semi conductor formed due to addition of acceptors.
Accuracy
The degree of
closeness of measurement value of a quantity to the expected value is called
accuracy. In other words, the extent to which a given measurement agrees with
the standard value for that measurement.
Achromatic Combination of Lenses
A lens
combination, for which the image of an object illuminated with white light is
distinctly obtained at the same place for all colors of light, is said to be an
achromatic combination of lenses.
Achromatic Lens
A lens
combination, for which the image of an object illuminated with white light is
distinctly obtained at same place for all colors of light, is said to be an
achromatic combination of lenses.
Achromatic Prism
A Prism composed
usually of two prisms which have unequal dispersive powers. They are combined
in such a fashion that a ray of light passed through them is refracted or bent
into a new position, but it is free from color.
Acoustic Impedance
It is the ratio
of acoustic pressure to acoustic volume flow. Acoustic impedance varies
strongly when the frequency of sound is changed. The acoustic impedance at a
particular frequency indicates how much sound pressure is generated by air molecules
vibration at that frequency.
Acoustics
The branch of
physics that deals with the process of generation, reception and propagation of
sound.
Actinides
Any of the series
of 15 metallic elements from Actinium (atomic number=89) to Lawrencium (atomic
no. 103) in the periodic table. They are all radioactive. The heavier elements
are extremely unstable and not of naturally occurring.
Actinium Series
Set of unstable
heavy nuclei which decay radioactively beginning with Actino-Uranium, isotope
of Uranium U-235 and end with Actinium D, constituting non radioactive isotope
Lead, of mass number 207.
Actinometer
It
is radiometric instrument used for measuring heating capability of radiation.
They are used chiefly for meteorological measurement of terrestrial and solar
radiation.
Activator
The
name assigned to the impurity atoms occurring in relatively small
concentrations in host material or a small stoichometric excess of host
material, which leads host material to exhibit phenomenon of Luminescence.
Active Device
It is a device
that requires a source of energy for its operation and has an output that is a
function of present and past input signals. Active devices are components that
are capable of controlling voltages or currents and create switching action in
the circuit.
Activity
The number of
nuclei of a given radioactive sample disintegrating per second is referred to
as activity of radioactive substance.
Acute Angle
Angle with a
measure between 0o & 90o.
Adhesion
It is the force
of attraction between molecules of different substances.
Adiabatic Demagnetization
It is the process
of cooling certain materials to extremely low temperatures down to milli
Kelvin. The process was first proposed by chemists Peter Debye (1926)
and William Francis Giauque. The process capitalizes on paramagnetic properties
of some materials (usually in gaseous form) to reduce their temperatures to
very low range. The process involves reducing temperature of sample (usually
gas) by keeping in contact with cold reservoir; with magnetic field induced in
it till thermal equilibrium is attained. After thermal equilibrium is attained,
magnetic field intensity is increased thus reducing entropy due to orderly
alignment of particles. After the isolation of sample from reservoir, the
magnetic field is reduced which results in still further reduction of temperature
by many fold.
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