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### PHYSICS DICTIONARY

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Earth

One of the nine planets revolving around sun and is third planet orbiting from sun. The distance of orbit from sun is 149,600,000Km and has diameter of 12,756.3Kms. It is the fifth largest of the planets. The Mass is about 5.97x1024 Kg

Echo

Repetition of sound produced due to reflection by a distant extended surface like cliff, hill, well, building etc., is called an echo. The effect of sound on human ear remains 1/10th of second. If sound reflects back in a time less than 1/10th of second, no echo is heard.

Eddy Current

When a metal body is moved in a magnetic field in such a way that the magnetic flux through it changes or is placed in a changing magnetic field, induced current circulates throughout the body.  They are called eddy currents.

Edge Dislocation

A linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra half plane of atoms within a crystal. The burgers vector is perpendicular to the dislocation.

Effective Mass of Electron

The mass of an electron inside crystal appears, in general, different from free electron mass and is referred to as effective mass. The effective mass can be greater or lesser than electron mass.

Efficiency of Engine

The ratio of useful work obtained by the engine in one cycle to the heat absorbed from the source is called efficiency of engine.

Effusion

Effusion is the process in which individual molecules flow through a hole without collisions between molecules. This occurs if diameter of the hole is considerably smaller than the mean path of molecules. According to Graham’s law, rate at which gas effuse is dependent on their molecular weight; gases with lower molecular weight effuse more quickly.

Eigen Function

It is wave function for a given physical system which contains measurable information about system.

Eigen Value

The word is derived from German word “Eigenwert” which means characteristic value. A scalar associated with a given linear transformation of vector space and having the property that there is some non zero vector which when multiplied by scalar is equal to vector obtained by letting the transformation operate on the vector.

Einstein Shift

In astrophysics, gravitational red shift or Einstein shift is the process by which electromagnetic radiation originating from a source that is in gravitational field is reduced in frequency, or red shifted, when observed in a region of a weaker gravitational field. This is a direct result of Gravitational time dilation - as one moves away from a source of gravitational field, the rate at which time passes is increased relative to the case when one is near the source. As frequency is inverse of time (specifically, time required for completing one wave oscillation), frequency of the electromagnetic radiation is reduced in an area of a higher gravitational potential (i.e., equivalently, of lower gravitational field). There is a corresponding reduction in energy when electromagnetic radiation is red-shifted, as given by Planck's relation, due to the electromagnetic radiation propagating in opposition to the gravitational gradient.

Einstein Theory of Specific Heats

A theory of the specific heat capacity of solids put forward by Albert Einstein in 1906, in which it was assumed that the specific heat capacity is a consequence of the vibrations of the atoms of the lattice of the solid. Einstein assumed that each atom has the same frequency. The theory leads to the correct conclusion that the specific heat of solids tends to zero as the temperature goes to absolute zero, but does not give a correct quantitative description of the low temperature behavior of the specific heat capacity.