Showing posts with label EVENT. Show all posts
Showing posts with label EVENT. Show all posts


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The “ether” is a hypothetically predicted matter to explain the phenomena of light, and to account for the flow of energy across empty space. The existence of which was not proved till date experimentally.

Euclidean Geometry

The study of plane and solid figures on the basis of axioms and theorems employed by Greek mathematician Euclid.


Process by which atoms or molecules of liquid gain sufficient energy and gets converted to gaseous state. There is no boiling involved.

Even-even Nucleus

Nucleus having even no. of neutrons and protons.

Even-odd Nucleus

Nucleus having even no. of protons and odd no. of neutrons.


A given point (x,y,z,t) in space time is called event.   


Prefix in the metric system denoting 1018 of a given base unit.

Excitation Energy

Energy required for exciting electron from lower energy state to particular higher energy state.


Process of transferring electrons or atoms from lower energy states to higher energy states.

Excited State

An electron energy state, not normally occupied to which an electron may be promoted by the absorption of some type of energy.


It is a bound state of an electron and hole which are attracted to each other by electrostatic Coulomb force. It is an electrically neutral quasi particle. It is regarded as an elementary excitation of condensed matter that can transport energy without transporting net electric charge.


See exothermic.


The outermost region of earth’s atmosphere, beginning at an altitude of approximately 550 km to 700 km and merging with interplanetary medium at around 10000 km. The exosphere consist chiefly Hydrogen and Helium at extremely low densities. Temperatures in earth’s atmosphere remain constant with altitude, averaging about 1500 K. The earth’s exosphere contains the Hydrogen, Geo corona and Van Allen radiation belts.

Exothermic Process

Chemical reaction in which there is release of energy in the form of heat, light or sound. These processes occur spontaneously. They result in high randomness of entropy of the system. They are denoted by a negative heat flow (heat lost to the surroundings) and decrease in enthalpy.

Exponential Function

An Exponential Function is a function of the form y = abx, where both a and b are greater than 0 and b is not equal to 1.


It is defined by ICRU (1980), as “the quotient of dQ by dm, where the value of dQ is absolute value of total charge of the ions of one sign produced in air when all the electrons liberated by photons in air of mass ‘dm’ are completely stopped in air (or) In simple terms, it is defined as total electric charge of the ions generated by the gamma radiation per given mass of air.

External Work

When the force is exerted by the system on its surroundings leading to displacement, then the work done is called external work.


It means attenuation of incident electromagnetic wave due to absorption by medium or attenuation by medium.

Extraordinary Ray

One of the two refracted rays from double refracting crystals which don’t obey laws of refraction is called as extra ordinary ray.


Extrapolation is an estimation of a value based on extending a known sequence of values or facts beyond the area that is certainly known.

Extrinsic Semiconductor

The semiconductors for which the electrical behavior is determined by impurities, which when present in even minute concentrations, introduce excess electrons or holes.


A forming technique where by a material is formed by compression through a die or orifice.

Eye Piece

Combination of Two lenses used in optical instruments such as microscope or telescope etc., to obtain image free from aberrations.


It is type of optical lens placed in optical devices near focal point of objective to magnify image. It is so named as it is usually closest to eye of observer using the optical device. 


An “event” is anything that happens at some definite locations at some definite time. Typical examples are your birth, assassination of Abraham Lincoln etc. In contrast, a forest fire that sweeps across 10000 acres in 5 days does not constitute an “event” because the fire is spread out in space and time.
The adjective “definite” means   “distinct” or  “limited” for any one observing the happening.

  • Spatially separated events that are simultaneous in one frame are, in general, not simultaneous when viewed from other reference frame.
  • Simultaneity is a relative concept, but not an absolute one.
  • The concept of simultaneity between two events in different space points has an exact meaning only in relation to a given inertial system i.e. “Each frame of reference has its own particular time”.
  • To measure the length of an object means to locate its end points simultaneously. As simultaneity depends on frame of reference, the length measurements will also depend on frame of reference.
  • Thus, “The length i.e. Space is a relative concept, not an absolute one”.
  • Thus there is no such thing as an absolute, global “now”.