Definition of Ampere

It is the constant current which, if maintained in two straight parallel conductors of infinite length and of negligible cross-section and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 x 10 ^ -7 N/m of length.

How is it proved that alpha rays are nuclei of Helium atoms?

The identification is made by Rutherford and Royds in 1909. By spectroscopic method, they found traces of Helium in a pure sample of Radon gas, which is an alpha emitter. When an electric discharge was passed through a tube containing pure radon gas, initially only characteristic Radon lines appeared.

After a day, Rutherford found that Radon lines became somewhat weaker and new lines started appearing. These new lines were identified with Helium spectrum. As the days passed, the Radon spectrum began weakening while Helium lines grow brighter.

Thus, for first time, people saw decay of an element (Radon) and birth of a new element, Helium nuclei. Such a transformation in which a parent element gives rise to a new element called daughter product by emitting radioactive rays is called radioactive transformation.

What are nano materials?

These are materials whose dimensions are less than 100nm. They act as one dimensional systems or zero dimensional.For comparison, a human hair is about 50,000nm in diameter, while a smoke particle is about 1000nm in diameter.

The term nano materials is less specific since it refers to coatings that are less than 100nm.

The nano particles consist only thousands of atoms. They are called quantum dots.

Methods of Synthesis of Nano Structured Materials:

Synthesis and assembly strategies can be accommodated from Liquid, Solid or Gas Phase

i) By employing chemical or physical deposition approaches.

ii) Relying on either chemical reactivity or physical compaction to integrate nano structure building blocks to form final nano material structure.  

Variety of techniques are
i) Assembling from nano building blocks
ii) Powder/Aerosol compaction
iii) Chemical Synthesis
iv) Mechanical attrition
v) Lithography/Etching

These above techniques can be classified into two approaches:

i) Bottom up Approach: Here first building blocks are formed and then assembled to form final material.

ex:- Aerosol /Powder technique in which powder components are compacted into final material.

This approach has been widely used in formation of structural composite materials.

ii) Top-Down Approach: Here first a suitable nano material is taken and then sculpted according to functionality of material. This approach is very similar to techniques employed semiconductor industries in forming devices from electric substrate by etching a pattern from it.Lithography/etching, Ball milling fall in this category.

Classification of Nano Crystalline Materials:

i) Nano crystalline materials are single phase or multi phase poly crystals, the crystal size of which is of order of few (1-100nm) is at least one dimension.

ii) They can be equiaxed and can be formed nano strucuture Crystallites -3D nano structures

iii) They can consist of lamellar structure and will be termed as layered nano structure-1D

iv) They can be filamentary in nature - 2D

v) They can be clusters or cluster assembly - 0D 

Why statistical mechanics was introduced?

When we consider bodies at macroscopic level they consist of uncountable atoms or molecules i.e about 10^23 atoms/gm mole. In such cases we cannot predict the result of interactions between atoms with the help of ordinary classical laws of motion. In order to solve such a situation, a new branch of science called statistical mechanics is introduced.

Statistical mechanics is the branch of science which establishes the interpretation of macroscopic behavior of system in terms of its microscopic properties. It doesn't deal with motion of each particle but it takes into account the average or most probable properties of system with out going into interior details of characteristics of its constituents.

The larger the number of particles in the physical system considered, the more nearly correct are statistical predictions.

Before the advent of quantum theory, Maxwell, Boltzmann, Gibbs etc applied statistical methods making the use of classical physics. These statistical methods are known as "classical statistics" or "maxwell boltzmann statistics".

These statistics explained successfully many observed physical phenomenon like temperature, pressure, energy etc; but couldn't explain adequately several other experimentally observed phenomenon like black body radiation, specific heat at low temperature etc.

In order to explain such phenomenon "quantum statistics" was introduced and developed by Fermi, Dirac, Bose, Einstein with new approach by using new quantum idea of discrete exchange of energy between system.

    

What is the reaction cross section for Helium-3 and boron-10 isotopes for thermal neutrons?

The reaction crossection for Helium-3 is 5330 Barns and that for Boron-10 is 3840 Barns.
Both the reactions are strongly  dependent on incident neutron energy 'E' and have roughly a 1/sqrt(E) dependence.

Small trick for designers using capacitors

Suppose you require a smaller capacitance with higher voltage rating for your application but you are left with only higher capacitance capacitor with less voltage rating. How could you overcome this problem?

You can follow a small trick. You put two or more capacitors in series to arrive at your designed capacitance of smaller value.Because
i) It divides the voltage over two capacitors and thus has net effect of doubling (in case of two capacitors) the voltage rating.
ii) It reduces overall capacitance by following

C = (C1*C2) / (C1+C2 )

where 'C' is total capacitance of two capacitors in series.

For instance, consider two capacitors 100 pF @500VDC,

Then keeping them in series we get C = 50pF

voltage is now divided over two capacitors so total rating is 50pF @1000V Dc.

Hope this is helpful for designers.