Showing posts with label mobility. Show all posts
Showing posts with label mobility. Show all posts


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 Drift velocity of charge carriers per unit electric field


If the same value appears a number of times in the data, this value is called mode.


It is referred as method of slowing down of neutrons in the range from fission energies to roughly below 1eV.


Substance used to reduce the energy of neutrons, called thermalization. Good moderator is a substance having low absorption crossection, low atomic weight and high scattering crossection.


 Substance which can slow down neutrons with minimum absorption. Generally moderators do shall have i) Large scattering crossection ii) Small absorption coefficient iii) Low atomic number


Process of sending electrical audio signal by superimposing it on high frequency carrier wave for easy transmission to longer distances.


The transmission of electrical energy radiatively is practicable only at high frequencies e.g., above 20KHz . In order to transmit audio signal properly, process of superimposing electrical audio signal on high frequency carrier wave. The resultant waves are known as modulation waves and process is called modulation.

Modulus of Elasticity

The ratio of stress to strain when deformation is totally elastic; it is measure of stiffness of a material.

Modulus of Resilience

The strain energy per unit volume required stress a material from an unloaded state up to the point of yield.   

Modulus of Rigidity

The ratio of tangential stress to shearing strain within the elastic limit is called rigidity modulus.

Molar Gas Constant

The molar gas constant, also known as the universal molar gas constant, is a physical constant that appears in an equation defining the behavior of a gas under theoretically ideal conditions. The gas constant is, by convention, symbolized R. The gas constant has been found, by experiment, to have a value of approximately 8.3145 Joules per Kelvin per Mole (J · K-1 · mol-1).

Molar Specific Heat

Amount of heat required to raise the temperature by one degree centigrade or one Kelvin.


Chemical quantity used to describe concentration of solute in solution. It is defined as no. of moles of solute per liter of solution.


Shaping a plastic material by forcing it , under pressure and at an elevated temperature  is called as a molding.


It is the quantity of a substance, which corresponds to Avogadro’s number i.e. 6.023 x 1023 atoms.   


Quantity of any substance whose mass, in grams is numerically equal to its molecular weight is called a mole.

Molecular Range

The maximum distance up to which a molecule exerts force of attraction is called as molecular range.

Molecular Spectrum

Spectrum which arises from rotation of a molecule as a whole and vibrations of its constituent atoms relative to one another as well as changes in its electronic configuration.

Molecular Weight

It is the sum of atomic weights of all atoms in a molecule.   


A molecule is the smallest particle in a chemical element or compound that has chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds.

Moment of Inertia

 It is the inertia of rotation of a body about the given axis.


Physical quantity which represents product of mass and velocity is called momentum.

Monochromatic Aberration

Aberrations formed in images formed by spherical mirrors and lenses when the source of light is monochromatic.

Monochromatic light

Technically light having single wave length is referred to as monochromatic wavelength. But no electromagnetic wave is purely monochromatic. Hence monochromatic light is said to have a wavelength within a short wavelength range.   


The two types of Internal Energy are

(i) The Vibrational energy of metallic atoms (ions) about mean lattice Positions.

(ii) The free energy (kinetic energy) of free electrons

The thermal properties of solids depend totally upon changes in the energy of Lattices and free electrons.

When an electric field is established across the metallic solid, the free electrons are accelerated. Their Kinetic Energy increases and of course a part of their energy is lost by collision with lattice atom.

The resulting flow of charge or current is directly proportional to velocity of electrons. This velocity is determined by applied electric field and also the collision frequency.

In the absence of an electric field, the electrons can move from place to place randomly in the crystal, without any change in the energy and collide occasionally with the atoms.In between two collisions, the electron may move with a uniform velocity ; but during every collision both direction and magnitude of velocity gets altered in general.

The average speed of this thermal motion depends on absolute temperature.

                         Fig: Zigzag motion of electron due to frequent collisions with atoms at lattices

The thermal velocities calculated may not bring any net transport of electric charges, since on average, for every electron moving in one direction there will be another moving in opposite direction.

When an electric field (e) is applied to a metals in which there are ’n’ free electrons per unit volume.

Acceleration of electrons = F/M = −eE/m 

Thus, an electron acquires additional non-random velocity opposite to direction of field. This velocity is responsible for transport of electrons in conductors.

The magnitude of drift velocity, is very much limited by the deceleration of electrons that jump in to Cations of lattices from time to time (or electron collisions with the cations act as frictional force)

Mobility is defined as drift velocity per unit electric field.
Now let there are ‘n’ no electrons per unit volume of a conduct as shown in fig