Showing posts with label Distance. Show all posts
Showing posts with label Distance. Show all posts

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> 

Dissociation

It is phenomenon of infinite separation of atoms of a molecule.


Distance of Closest Approach

It is the distance from the nucleus of an atom at which the alpha particle comes to rest and its kinetic energy is totally converted into electrostatic potential energy.


Distance

It is the total length of actual path covered by a moving body.


Distortion

The image of a plane square like object placed perpendicular to the principal axis is not of the same geometrical shape as the object. This aberration is called as distortion and arises due to variation of magnification with lateral distance of an object point from the axis of lens.


Diathermanous

Substances which are transparent for thermal radiations are called the diathermanous.


Divergence

It represents the total amount of flux escaping an infitesimal volume at a point in vector field.


D-lines of Sodium

The bright doublet (line spectrum) which is responsible for yellow light from Sodium lamp is called as D-lines of sodium. The line emission spectrum of lamp consists of two wavelengths 5890 Ao & 5896Ao. The transition which gives rise to doublet is from 3P3/2 & 3P1/2 to 3S1/2 levels. The doublet is due to splitting of 3P level into state with angular momentum 3/2 & 1/2 by magnetic energy of electron spin in presence of internal magnetic field caused by orbital motion of electron.  


Domain Theory

Theory in magnetism as per which any ferromagnetic or ferri-magnetic material that is at a temperature below curie temperature, is composed of small volume regions in which there is mutual alignment in the same direction of all magnetic dipole moments. Such a region is called a domain, and each one is magnetized to its saturation magnetization. Adjacent domains are separated by domain boundaries across which the direction of magnetization gradually changes. Normally, domains are macroscopic in size and for polycrystalline specimen; each grain may consist of more than a single domain. Thus, in a macroscopic piece of material, there will be large number of domains, and all may have different magnetization orientation. The magnitude of magnetization field for entire solid is vector sum of magnetizations of all domains, each domain contribution being weighted by its volume fraction.


Donor

It is an impurity atom when added to host crystal lattice (semiconductor), contributes an electron to conduction bond after formation of covalent bonds with four valence electrons.


Doping

The intentional addition of foreign atoms (acceptors/donors) into semiconductor with controlled concentrations. 


Doppler Effect (Light)

Change in frequency of light radiation when source or observer move with respect to each other.


Doppler Effect (Sound)

Apparent change in the pitch of sound due to relative motion between source and observer is called as Doppler effect.


Dose (Radiation)

Materials other than air exposed to ionizing radiation will differ in their rate of energy absorption. It is therefore necessary to have a standard for defining energy absorption by ionization in different materials. The quantity for this purpose is called absorbed dose ‘D’ and measures energy deposited by ionizing radiation per unit mass of material. The SI unit is Gray equal to absorption of     1 joule per Kg of material.


Dose Equivalent

The effect of a particular radiation on a biological system depends on absorbed dose ‘D’ and on quality factor ‘QF’ of radiation. Dose equivalent is product of

D & QF.


Dosimeter

Device which measures absorbed dose deposited in its sensitive volume by ionizing radiation.


Dosimetry

Subject which deals with measurement of absorbed dose or dose rate resulting from interaction of ionizing radiation with matter.


Dot Product

Dot product of two vectors is the product of the magnitudes of two vectors and cosine of angle between them.


Double Refraction

Some crystals have the property that the light rays incident on them splits into two refracted rays inside the crystal. The property is called double refraction.


Doublet

Combination of two simple lenses is called as doublet. 


Drift Tube

It is used in linear accelerator in which there is arrangement of dynodes at varying potential to drift electrons to higher velocities.


Drift Velocity

Velocity attained by charge carriers under influence of electric field. The velocity is directly proportional to electric field and inversely proportional to mass.


Dry Bulb Temperature

It is the temperature which is usually referred to as simply ambient air temperature.


Dry Cell

It is a galvanic electric cell in which the chemicals in the electrolyte are made into a paste such as ammonium chloride and manganese dioxide so that they cannot easily spill from their container. A chemical reaction within the battery creates an electrical charge that flows from inside to an outer circuit that is connected to an electrical device.

Difference between Distance & Displacement

Displacement is a vector quantity as it is associated with direction,but distance is a scalar quantity which does not give any information about direction of motion.Distance and displacement magnitude are numerically equal only when the body travels in a straight line from A to B(i.e the shortest distance from a point to another). Also distance has always a non-zero magnitude,but displacement can be zero if the body returns to the point of origin at the end of motion.