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>
D’Alembert
Principle
It is alternative
form of Newton’s second law of motion which has been named after its
introducer, French physicist Polymath Jean Le Rond D’Alembert. It states that
difference between forces acting on a system of mass of particles & time
derivatives of momentum of system itself along any virtual displacement
consistent with constraints of system is zero.
Daltons
Law of Partial Pressure
Law proposed by
John Dalton in 1801 which states that “the total pressure exerted by the
mixture of non-reactive gases is equal to the sum of partial pressures of
individual gases.
Damped
Vibration
When pendulum
vibrates in air medium, there are frictional forces and consequently energy is
dissipated in each vibration. Thus amplitude decreases continuously with time,
and finally oscillations die out. Such vibrations are called damped
vibrations.
Damping
It is phenomenon
of dying out of mechanical or electrical oscillations due to external forces.
Daniel
Cell
It was invented
in 1836 by john Fredric Daniel, a British chemist. It is a type of cell having
a zinc anode in dilute Sulphuric acid separated by a porous barrier from a
copper cathode in copper Sulphate solution. The principle behind the cell is
that a liquid solute called electrolyte between metal plates begins to dissolve
zinc and copper into positively charged ions as ions leave the metal, free
electrons remain behind. The zinc dissolves more rapidly than the copper, which
means that the zinc soon contains more electrons. If one connects two pieces of
metal with a wire the electrons will migrate through the wire from zinc to
copper, creating electric current.
Dark
Matter
Hypothetical
predicted matter by astrophysicists, which is not seen directly by telescopes.
The unaccounted missing mass is termed as dark matter. It neither emits nor
absorbs light. It was first postulated by John Oort in 1932.
Davisson
Germer Experiment
In 1927, Clinton
J. Davisson and Lester H. Germer confirmed experimentally the wave nature of
electrons by bombarding a nickel target with electrons and measuring the
intensity of electrons scattered from target. Davisson and Germer determined
wavelength of electrons from known atomic separation and the measured Bragg
angle at which the electron intensity exhibited a maximum. They found that the
wavelength calculated is well in agreement with electron wavelength calculated
from debroglie relationship. Davisson and Germer experiment demonstrated
diffraction of electrons and gave evidence of wave nature of electron.
Day
Unit
of time defined as interval equal to 24 hours.
(or)
The interval of light between two successive
nights; The time between sunrise and sunset.
Debroglie
Wave
Wave nature attributed to particle.
Debroglie
Wave length
Ratio of Planck’s
constant to momentum of particle.
Debroglie’s
Hypothesis
Hypothesis put
forward by French scientist Debroglie, as per which materialistic particle
possess both wave and particle characteristics. The wave and particle nature
for matter are complimentary in nature.
Debye
Theory of Specific Heats
A theory of the
specific heat capacity of solids put forward by Peter Debye in 1912; in which
it was assumed that the specific heat is a consequence of the vibrations of the
atoms of the lattice of the solid. In contrast to the Einstein theory of
specific heat, which assumes that each atom has the same vibration frequency,
Debye postulated that there is a continuous range of frequencies that cuts off
at a maximum frequency, which is characteristic of a particular solid. The
theory leads to the conclusion that the specific heat capacity of solids is
proportional to T3, where T is the thermodynamic temperature. This
result is in very good agreement with experiment at low temperatures. The Debye
temperature is characteristic of a particular solid.
Debye
It
is unit of electric dipole moment.
1
Debye = 3.33 x 10-30 Coulomb-meter
