PHYSICS DICTIONARY

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Electron Affinity

Amount of energy released when an electron is added to element to create anion.

Electron Diffraction

Electron diffraction is a collective scattering phenomenon with electrons being (nearly elastically) scattered by atoms in a regular array (crystal). This can be understood in analogy to the Huygens principle for the diffraction of light. The incoming plane electron wave interacts with the atoms, and secondary waves are generated which interfere with each other. This occurs either constructively (reinforcement at certain scattering angles generating diffracted beams) or destructively (extinguishing of beams). 

Electron Gas

Free electrons behavior in vacuum or metallic conductor.

Electron Gun

Arrangement to produce a fine beam of electrons accelerated to desired velocity.

Electron-Ion Pair

Ionization is the process of removing one or more electrons from a neutral atom. This results in the loss of units of negative charge by the affected atom. The atom becomes electrically positive (a positive ion). The products of a single ionizing event are called an electron-ion pair.

Electron Lens

It is a system which uses both electric and magnetic fields to focus a beam of electrons.

Electron Mass

Rest mass of electron is one of the fundamental constants of Physics. It is the mass of rest electron, the value of which is  9.11x10^-31 Kg or ~ 0.51MeV/C².

Electron Microscope

The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen. It is capable of much higher magnifications and has a greater resolving power than an optical microscope, allowing it to see much smaller objects in free details.

Electron Microscopy

Technique used to study the microstructure details of crystalline specimen. Electron microscope is capable of obtaining higher magnification. An image of structure under investigation is formed using beams of electrons instead of light radiation. According to quantum mechanics, a high velocity electron will become wave like, having a wavelength that is inversely proportional to its velocity. When accelerated across large voltages, electrons can be made to have wavelengths on order of 0.003nm. High magnifications and resolving powers of these microscopes are consequences of shorter wavelengths of electron beam. The electron beam is focused and image is formed with magnetic lens. Both transmission & reflection beam modes of operation are possible.    

Electron Spectroscopy

Electron spectroscopy is an analytical technique to study the electronic structure and its dynamics in atoms and molecules. In general, an excitation source such as X-rays, electrons  or synchrotron radiation will eject an electron from an inner-shell orbital of an atom. Detecting photoelectrons that are ejected by X-rays is called X-ray Photoelectron Spectroscopy  (XPS) or electron spectroscopy for chemical analysis (ESCA). Detecting electrons that are ejected from higher orbitals to conserve energy during electron transitions is called Auger electron spectroscopy (AES).

Electron Spin Resonance (ESR)

The paramagnetic substances which contain unpaired electrons when subjected to a magnetic field, the energy levels corresponding to an electron will split up. When we apply an oscillating field in perpendicular direction whose frequency lies in microwave region then resonance occurs and electrons in lower energy state will absorb energy giving rise to absorption spectra. The spectrum is known as ESR.

Electron State

It is one of a set of discrete, quantized energies that are allowed for electrons. In the atomic case, each state is specified by four quantum numbers.

Electron Volt

The energy gained by electron when put under potential difference of 1 volt. It is equal to 1.6 x 10^-19 J.

Electronics

Branch of applied physics, which deals with devices made of semi-conductor materials having electrons/holes as charge carriers. The branch includes study and application of active/passive devices for various scientific and technology applications.

Electroplating

See electro deposition.

Electropositive

Chemical property which describes tendency of an atom to lose valance electrons.

Electroscope

It was the first electrical measuring instrument used to detect presence and magnitude of electric charge on a body.

Electrostatic Lens

Device used to focus electron beam.  

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Electronegativity

Chemical property which describes tendency of an atom to accept electrons.

Electroplating

 See electro deposition.

Electroscope

An instrument which was first invented by William Gilbert in 16^th century, used to detect electric charge and measure its magnitude.

Electrostatic Precipitation

A process that removes suspended dust particles from a gas by applying electrostatic charge to the particles and collecting them on charged plates.

Electrochemical Cell

Arrangement in which two different metals are placed in conducting liquid called as electrolyte, with electrical potential difference between them. A pair of different metals arranged in this way is an electrochemical cell. This arrangement transfers chemical energy to electrical energy.

Electrodynamics

The quantum mechanical laws combined with laws of electricity came to be known as special branch called electrodynamics.

Electrolysis

The phenomenon which occurs in electrolytic cells involving breaking of electrolytes when electric current is passed through them.

Electrolyte

A solution through which an electric current may be generated by motion of ions.

Electromagnetic Radiation

Radiation which propagates in the form of wave in which electric field and magnetic field lies perpendicular to each other and also to the direction of propagation.

Electromagnet

It is a device consisting of a core of magnetic material such as iron, surrounded by a coil through which an electric current is passed to magnetize the core. Electromagnets are particularly useful where ever controllable magnets are required, as in devices in which the magnetic field is to be varied, reversed, or switched on and off. Other devices that utilize electromagnets include particle accelerators, telephone receivers, loudspeakers, and televisions.

Electromagnetic Induction

Phenomenon in electromagnetics as per which “any electric field that changes over time will produce a magnetic field in the space around it” and “any magnetic field that changes over time will produce an electric field in the space around it “.

 

Electromagnetic Interaction

The type of interaction between two charged particles by exchange of photons is called as electromagnetic interaction. The strength of electromagnetic interaction is given by dimensionless fine structure constant α = 1/137 and is due to photon exchanges. 

Electromagnetic Spectrum

Electromagnetic radiation fall in wide range from gamma rays (emitted by radioactive materials) having wavelengths on the order of 10^-14 meter, through x-rays, UV, Visible, Infrared and radio waves with wavelengths as long as 10⁵ meter.

Electromagnetic Theory

The theory which aims at explaining combined effect of electric & magnetic fields. This theory considers electric & magnetic force as different facets of more fundamental force. The most basic idea in electromagnetic theory is “a changing electric field generates a magnetic field” and “a changing magnetic field generates a electric field.” These principles are quantified by Maxwell’s equations, named for James Clerk Maxwell, the Scottish physicist and mathematician whose work in the 19th century established the discipline by revolutionizing how physicists conceived of light. The success of electromagnetic theory led to the collapse of the rest of Newtonian physics in the 20th century.

Electromagnetism

It is branch of physics which deals with electricity and magnetism, their interaction with each other and with electric charges and currents. Michael Faraday showed in 1831, that a changing magnetic field can induce a current in a circuit, and James Clerk Maxwell predicted that a changing electric field has an associated magnetic field.

Electrometer

High sensitive instrument used to measure electric charge or potential difference.

Electromotive Force

It is the work done on unit positive charge in taking it through low potential end to high potential end.

Electromotive Series

A ranking of metallic elements according to their standard electrochemical cell potentials.

Electron

It is an elementary particle classified as Lepton, having spin ½, negatively charged and which interacts weakly with other particles. 

(or)

It is a subatomic particle which carries a negative charge and is considered as the basic unit of electric charge. The rest mass of the electron is 9.109 × 10⁻³¹ kg. It is the basic unit of electric charge having value of 1.6 x 10^-19 Coulomb.

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Einstein

It is unit of energy used in photo chemistry. One Einstein is energy per mole of photons carried by a beam of monochromatic light.

One Einstein= 3.99 x 10^-10 ν, Joules per mole; ν is frequency

Einstein’s Mass-Energy Relation

The total energy of a moving body is equal to relativistic mass times the square of speed of light. E=mc²; ‘m’ is mass of body in motion; m= m_o/sqrt(1-v²/c²); m₀ is rest mass of body; C is velocity of light.  

Elastic Collision

It is the type of collision in which both the momentum & kinetic energy are conserved and colliding bodies do not undergo any deformation.

Elastic Deformation

The deformation in which stress and strain are proportional is called elastic. In such a deformation, when applied load is released, the substance returns to original shape.

Elastic Fatigue

The state of temporary loss of elastic nature of a body due to repeated stress over a long time interval is called as elastic fatigue.

Elastic Limit

When the strain is increased slightly beyond proportionally limit in a wire, the stress is not proportional to strain. However the wire exhibits elastic property. When deforming force is removed, wire regains natural wavelength. This is called elastic limit. 

Elasticity

It is the property of a body by virtue of which it tends to regain its original size and shape after removal of deforming forces.

Elastomer

A polymeric material that may experience reversible elastic deformation.

Electret

The word is first coined by Oliver Heaviside in 1885. It is derived from words electricity (electr) and magnet (et). It is dielectric material that has a quasi permanent electric charge or dipole polarization.        

Electric Current

It is the amount of charge flowing through a particular area in unit time         

Electric Field

There exists a region around any charge, filled with imaginary lines of force. The electric field is defined as force acting on any test charge placed in that region.

                                                (or)

It is defined as torque exerted on test dipole placed in that region. 

Electric Potential

Potential energy which a unit charge would have, if brought to a specified point in space from some reference point.

Electric Susceptibility

It is proportional constant between microscopic property “polarization” and macroscopic property “electric field”.

Electrical Discharge

It results from creation of conducting path between two points of different electrical potential in the medium, in which the points are immersed. Usually the medium is gas. It occurs when potential difference is very high.

Electricfield Intensity

Physical quantity used to measure strength of electric field in the space around a charged object. It is defined as force per unit charge placed at a point in the field.  

Electrodeposition

It is also known as electroplating. It is the process of depositing material on to conducting surface from a solution containing ionic species, by passing electric current.

Electroluminescence

The phenomenon in which electric energy can be used to generate photoemission in a solid is known as electro luminescence. 

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Ductility

It is the mechanical property which is a measure of degree of plastic deformation that has been sustained at fracture. It is expressed quantitatively as either percent elongation or percent reduction in area from a tensile test.

Dulong & Petit’s Law

It is the law which states that the atomic heat capacity for all solids is same and is nearly equal to 25 Jmol^-1K^-1 and is independent of temperature. 

Dwarf Star

It is small and low mass star that emits relatively less amount of light.  Most dwarf stars, including sun, burn their hydrogen at a much slower rate than giant and super giant stars and are consequently less luminous and have longer life spans that those main sequence stars do.

Dynamics

The branch of classical mechanics that is concerned with effects of forces on motion of a body or system of bodies, especially of forces that do not originate within the system itself is called as dynamics.

Dynamo Meter

Device used for measuring the force or torque or power available from a rotating shaft.

Dynamo

 It is an electrical device which converts mechanical energy into electrical energy utilizing the phenomenon of electromagnetic induction.

Dyne

 It is unit of force specified in CGS system of units.

1 dyne = 10^-5 Newtons