PHYSICS DICTIONARY

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Enthalpy

It is heat function at constant pressure. Mathematically expression is H=U+PV; ‘U’ is internal energy; ‘P’ is pressure and ‘V’ is volume.


Entropy Maximum Principle

For an isolated system in state of equilibrium, the entropy attains maximum value and remains constant.


Entropy

The thermal property which remains constant during adiabatic process is called entropy.

(or)

 Measure of randomness or disorderliness of molecules.

(or)

 Index of unavailable energy of a system.


Epicenter

The point on the surface directly above the “focus” is called Epicenter.


Epitaxial Growth

The technique of growing an oriented single crystal layer on a substrate wafer is called epitaxial growth. The substrate crystal may be a wafer of same material as the grown layer or a different material with similar lattice structure. The methods which are adopted for this growth are i) Chemical vapor deposition. ii) Liquid phase epitaxy iii) Molecular beam epitaxy


Equal Apriori Probability

A fundamental postulate of statistical mechanics is that a macroscopic system in equilibrium is equally likely to be in any of its accessible microscopic states satisfying macroscopic conditions of system.

                                               (or)

The probability of finding the phase point for given system in any region of phase space is identical with that for any other region of equal extension or volume. 


Equation

A mathematical statement or formula which shows the equality of two expressions.


Equation of Continuity

For any incompressible & non-viscous fluid flowing steadily, the product of its velocity and area of crossection at all points during its flow through a tube remain constant.  Velocity of fluid is inversely proportional to area of crossection.


Equation of Motion of Rigid Body

Relationship between torque applied to rigid body and angular acceleration of body is known as equation of motion of rigid body.


Equation of State

An equation of state is a relation between state variables. It is a thermodynamic equation which describes the state of matter under a given set of physical conditions, typically relating energy, temperature, volume, and pressure. Equations of state are most commonly used to describe properties of fluids, such as liquids, gases and plasma though equations of state may also be applied to solids.


Equilibrium of a Rigid Body

If a rigid body is subjected to number of forces acting on it and has neither translatory nor rotatory motion, then it is said to be in equilibrium. Following conditions are satisfied in such a case:

i)      The algebraic sum of forces acting on it is zero (translational equilibrium)

ii)    The algebraic sum of moments of all the forces about any point is zero.(rotational equilibrium)


Equilibrium (Phase)

The state of system where the phase characteristics remain constant over indefinite time periods is called as equilibrium. At equilibrium the free energy is least. 


Equipartition of Energy

The theorem of equipartition of energy states that molecules in thermal equilibrium have same energy associated with each independent degree of freedom of their motion.


Equipotential Surface

Surface on which every point is at same potential and the electric field is at right angles to all these points.


Erecting Lens

An eye piece sometimes used in Kepler telescopes that consists of four lenses and provides an erect image, which is more convenient for viewing terrestrial objects than the inverted image provided by simpler eye pieces. 


Erecting Prism

It is a system of prisms that converts the inverted image formed by most types of astronomical telescopes to an erect image, also known as inverting prism.


Erg

It is unit of energy in CGS system of units. It is amount of work done by a force of one dyne exerted for a distance of one centimeter. 1erg=10-7 J.


Ergodic Hypothesis

The time average of some property of a system in equilibrium is same as instantaneous ensemble average.


Error

The difference between measured value and true value is called as error.


Escape Velocity

It is the minimum velocity with which a body should be projected from the surface of the planet so as to escape its gravitational field.

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