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Nano Materials

Materials whose dimensions are less than 100 nm.

Natural Frequency

 Frequency of system when set in free vibration.

Natural Logarithm

A logarithm to the base ‘e’ which is irrational and whose value is equal to 2.71829. It is represented as log eX.. It is also called as Napier logarithm.


 A visible, thinly spread cloud of interstellar gas and dust. Some nebulae are remnants of supernova explosion others are gravity induced condensations of gases in interstellar medium which in certain cases may become a site for formation of new stars. The term was formerly used of any hazy , seemingly cloud like object, including what are now recognized as other galaxies beyond milky way, it is restricted now to actual clouds of gas and dust within our own galaxy.

Negative Feedback

When feedback energy is out of phase with input signal and opposite to it, then it is called negative effect.


Term used for electron when it is necessary to distinguish between electrons and positrons.

Neptunium Series

It is a radioactive series that does not now occur in nature and that begins with Plutonium of mass number-241 and continues to Americium to the longer lived member of series i.e. Neptunium of mass number 237, and eventually to stable end product Bismuth. 


An elementary particle introduced by Pauli in 1952. It was introduced in weak interactions involving beta decay to avoid violation of law of conservation of energy and angular momentum. It has solved mystery of variable energy of beta particles in beta decays.


Neutron Diffraction

 It is a non destructive technique that is used to probe the structure of materials at the atomic level. The sample is placed within a neutron beam and the angles at which the neutrons are deflected or scattered by material are recorded to generate a  “diffraction pattern” from which structural information can be extracted. Diffraction occurs when the neutrons encounter atomic nuclei or magnetic diploes within the sample. With an effective wavelength of 0.1-20 nm, thermal neutrons are ideally suited for probing atomic scale structures with high resolution. As neutrons do not possess an electric charge, they readily pass through matter regardless of local charge distribution. In consequence, a neutron beam is capable of penetrating well beyond surface of a sample, to a depth of few centimeters in most condensed phases. The technique is widely used in engineering for stress mapping and to examine mechanical behavior of materials and engineering components.

Neutron Flux

The neutron flux (φ) measures the intensity of neutrons passing through a cubic centimeter of material. It is given by: φ= nv; where n is the density of neutrons (the number of neutrons per cm3) and v is the speed of the neutrons. The unit for neutron flux is

In physical terms, the quantity ‘φ’ is the total distance traveled in one second by all the neutrons in the one cm3 volume, since it is obtained by multiplying the number of neutrons in that cm3 by the speed each is travelling. This is equivalent to the total length of all the neutron tracks laid down in one cm3 in one second. The expression for neutron flux applies to any neutron energy. When applied to thermal neutrons the product is known as the thermal neutron flux.  


It is SI unit of force. It is force required to accelerate a mass of one kilogram one meter per second per second. 

Newton’s First Law

Everybody continues in its state of rest or of uniform motion in a straight line unless it is compelled by an external force to change that state.

Newton’s Law of Cooling

The rate of loss of heat of a hot body (or rate of cooling of body) is directly proportional to mean excess of temperature of hot body over that of its surroundings.

Newton’s Second Law

The rate of change of momentum of a body is directly proportional to external force acting on it and takes place in the direction of force.

Newton’s Third Law

For every action, there is equal and opposite reaction.


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