Chemical laser and tunable laser.

In a chemical laser instead of atoms the molecules are brought in the metastable state by a chemical reaction. These lasers are very strong and efficient. In a chemical laser, hydrogen and fluorine gases combine to form the  hydrogen fluoride gas. It is used to obtain an infrared laser beam of nearly 2 MW power.

Another chemical laser is the carbon dioxide laser. It is used to obtain a laser beam of nearly 100w power. Its main application is in sergery to close he small blood vessels while cutting the tissues by the evaporation of water the through the infrared beam. In the industrial area carbon lasers of more power are used for cutting the metal sheets.

The other chemical lasers me the dye lasers in which organic dyes are used. The energy levels of molecules of these dyes close due to which are very Laser beam can be obtained from them in a continuous range of wavelength. The Wavelength range of these lasers is from the visible region to the infrared region. By changing the separation between the mirrors at the two ends of the resonant cavity, a dye laser can be tuned for the desired of wavelength range. This is why the dye lasers are also called the tunable lasers.

What is Dielectric ?

Dielectric- Material such as glass ceramics polymers and paper are non-conducting materials. They prevent flow of current through them. Therefore they can be used for insulative purposes when the main function of non-conducting materials is to provide electrical insulation they are called insulators. When non-conducting materials are placed in an electric field. they modify the electric field and themselves undergo appreciable changes as a result of which they act as stores of electrical chages. When charge storage is the main function the materials are called dielectrics. For a material to be a good dielectric, it must bw an insulator. Hence any insulator is a dielectric.

Physical process of depletion layer.

Physical Process of Depletion Layer- We know that a p-type materials has holes as majority carriers negatively charged impurity atoms called negative ions (or acceptor ions). The n-type material has free electrons as  majority carriers and positively charged impurity atoms called positive ions (or donor ions). When we combine these two materials, following process takes place-

(i)The holes from p-region diffuse to the n-region where they combine with the free electrons.
(ii) The free electrons from the n-region diffuse to the p-region where they combine with holes.
(iii) The diffusion of holes (from p-region to n-region) and free electrons (from n-region to p-region) takes place due to the reason that there is a difference of concentrations in the two regions. (iv) The diffusion of holes and electrons across the junction takes place for a short time. After a few recombination of holes and free electrons in the vicinity of the junction, a restraining force is automatically Setup This force is produced due to depletion région. which exists on either side of the junction. As result of this further diffusion of holes and free electrons from a one region to the other is stopped by this depletion layer.

Motion of charged particles in crossed electric and magnetic fields.

When Uniform electric and magnetic fields are perpendicular to ed oderand act over the same region they are said to be in crossed configuration. When electrons pass through the region, they are defected simultaneously both the fields. Let two charged plane parallel plates set up a uniform ele field E in the y-direction and a uniform magnetic induction B is also set up the same region between the plates in z-direction. The magnetic feld is sud to act into the page. The fields are so oriented that they are perpendicular to the direction of motion of electrons which is say, x-direction. Let a Step lectrons enter the crossed field configuration with a velocity v.
The electric field deflects the electrons upward where as the m field deflects them downward.
The force due to the electric field is and the force due to due to the electric field is -
FE=eE.

Limitetions of Geiger Muller.

One main disadvantages of G.M. counter is its dead time. Dead time refers to the time taken by the tube to recover between counts. it require about 200 IS for the tube to recover Ifa lot of particles enter the G.M. tube of rapid rate, the tube will not have time to recover and some particles may nd be counted.

History of Superconductivity.

Superconductivity is a state exhibited by many conductors when cooled below their superconducting transition temperatures. Superconductivity is one ofthe most fascinating physical phenomena having a vast potentiality in practical applications. A superconducting material exhibits zero electrical resistivity and complete diamagnetism. The superconducting state is influenced by temperature, magnetic field, and current. There exist critical values for these three parameters above which values the material passes into normal State.

In 1908, the Dutch Physicist Kammerlingh Onnes succeeded in his efforts to liquefy helium, Gaseous helium turned into liquid helium at 4.2K at atmospheric pressure. Using liquid helium as the coolant the variation of  electrical resistance of metals at low temperatures was studied by Chines In one theory, the electrical resistance of pure metals should decrease continuously and vanish at absolute zero temperature. In another theory it was expected to increase exponentially as temperature approaches 0K. However, in the year 1911, onnes discovered that the electrical resistance of highly purified mercury dropped abruptly to zero at 4.15 K. Sudden drop in resistivity was not in accordance with the expectations and was recognized by Onnes to be an emirelynew phenomenon. He called it superconductivity Subsequently super conductivity was discovered in lead. tin, zinc, aluminium and other metals as well as in a number of alloys.

What is Soler cell?

solar cell is a device which is used for converting radiation energy into electrical energy. These cells generate a voltage proportional to electromagnetic radiation intensity and are called the photovoltaic cells because of their voltage generating capability.
selenium and silicon are the most widely used materials for solar cells though gallium, arsenide, indium, arsenide, and cadmium sulphide are also used. The construction and cross-section of a typical power solar cell for use as an energy converter. The surface layer of p-type material is extremely thin so that light can penetrate to the junction. The nickel-plated ring around the p-type material is the positive output terminal and the plating at the bottom of the n-type material is the negative output terminal, Power solar cells are also available in flat strip for efficient coverage of available surface area.

Band theory of solids in solid state physics

On the basis of the classical free electron theory, electrical conduction Can occur in solid available. On the other hand, according a if free electrons are o band theory electrical conduction can take place in solid only if(i) a good number of free electrons are present and (ii) vacant levels are available immediately above the occupied energy levels Free electrons can absorb energy from the current source only inhere are unoccupied energy levels nearby gaining energy they jump into the empty levels giving rise to an electric current It describes that a partially filled band is required for causing electrica conduction.

Comparison between shell model and liquid drop model.

A comparative study between the single particles shell model and the liquid drop model according to Niels Bohr is that both are in conflict it each other In the shell model, it has been assumed that each nucleon moves in its orbit within the nucleus, independently of all other nucleons. The orbit determined by a potential energy function V(r). Each nucleon is regarded as an independent particle and the interaction between nucleons is considered to be a small perturbation on their action between the orbital nucleon and the rest is very weak in the liquid drop model,on the otherhand the nucleons are considered to interact strongly with each other so that the collective motions are possible. The following three examples speak infavour ofsuch collective motions-
(1) The phenomenon of nuclear fission which can be easily descr in terms of free vibrations of a liquid drop.
(2) The large values of electric quadruple moment in some nude cannot be accounted for on the single particle shell model. The discrepancy between the theoretical be explained only on de and experimental values can assumption that collective distortions nuclear core involving many of the nucleons also contribute to the quadruple moment.
(3) The third example is observed mean lines for ramna radiation of the electric quadruple type.
The observed lines are approximately 100 times shorter than estimated on the assumption that moves during the transition. This only one proton suggests that changes in the deformation of the core are involved.

What are salient features of liquid drop model of nucleus?

There are two important models proposed to explain the behavior and properties of the nucleus. They are liquid drop model and the shell model.
The liquid drop model was proposed by Niels Bohr in 1936, based on e external analogy between the nucleus and a liquid drop. Short range intermolecular forces operate in a liquid drop. The surface molecules at attracted to the inner molecules and the result is surface tension because of which the liquid drop takes spherical shape. The molecules in the liquid drop are in random motion and frequently collide with each other. The nudes possesses similar properties. The nucleons in a nucleus are in rapid motion and undergo frequent collisions. Each collision between nucleons involves an exchange of energy and momentum between them. If a certain amount of energy is imparted to the nucleus it gets excited me energy gets redistributed rapidly between the nucleons due to their mutual collisions. Some ofthe energy may be transferred to a surface nucleon. If energy of the nucleon is greater than its binding energy in the nucleus, the nucleon overcomes the nuclear forces and leaves the nucleus. The expulsion of a nuclear particle from the nucleus is similar to the evaporation of a molecule from a liquid drop.

Junction Breakdown

In case of reverse bias, a point is reached where application of too much negative case voltage will result in a sharp in the characteristic.
     At this point junction breakdown and current increases at a very rapid rate in a direction opposite to voltage region The reverse bias voltage that results in this dramatic change in character is called "Breakdown Potential" or " Zener Potential" and this sharp change in characteristics at any level is called zener region. It is found that once breakdown has occurred, very little further increase in voltage is required to increase the current to relatively high value. The junction itself offers almost zero resistance at this point.
The breakdown voltage depends on the width of the depletion region which, in turn, depend on doping level. There are two Dypes of breakdown:
(1) Zener Breakdown
(2) Avalanche Breakdown.

Why Si and Ge are used in semiconductors ?

Si and Ge are the two materials that have received the broadest range of interest in the development of semiconductor devices. The reasons for this are as follows:
(1) They can be manufactured to a very high purity level. In fact recent advances have reduced impurity levels in pure material to one part in 10 billion (1:10 000,000,000)
(2) The addition of one part of impurity (of the proper types) per million in a wafer of silicon material can change that material from a relativity poor conductor to a good conductor of electricity.
(3) Their characteristics can be altered significantly through the application of heat and light an important consideration in the development of heat and light sensitive devices.

Structure of ATOM

As you are aware, the atom is composed of three basic particles:
(a) Electrons
(b) Protons
(c) Neutrons 
Protons and Neutrons form the central portion ofthe atom which is called Nucleus while electrons move in approximately elliptic orbit about the nucleus. The mass of the protons and neutron is approximately same The difference between the two is that the proton is a positively charged particle and neutron is an electrically neutral particle.
          The electrons which revolve around the nucleus are very light in weight. An electrons is 1850 times lighter than a proton orneutron, this is because almost total mass of an is concentrated in its nucleus. Also electrons are negatively charged particles atom. The number of orbiting electrons are always equal to number of protons for any atom thus making atom electrically neutral.

What is fermi level ?

Fermi level is defined as the energy state or level which has a 50% probabilis of being filled by an electron.
For pure semiconductor, the Fermi Level lies midway between conduction band and valence band asshown in fig. At an absolute temperatureT=0 K, all energy states above the fermi level are empty and all energy states below fermi level are occupied. As the temperature increases some covalent band breaks up and such electrons go to the conduction band. Due to this, the fermi level shifts upward as the temperature increases.

Applications of Zener diode.

Applications of Zener Diode-
(i) It is used as a voltage regulator which gives a constant voltage from a source whose voltage may vary over suficient range.
(ii) It is used as a fixed reference voltage in transistor biasing circuits.
(iii) In waveshaping circuit, zener diode is used as limiter.
(iv) A Zener diode protect a meter movement or circuit against damage from an accidental application of excessive voltage.
(v) zener diode can produce a sudden change from low current to high current, so it is useful for switching operation.

What is optic axis ?

Optic Axis- Uni-axial crystals have a direction along which ordman and extra-ordinary rays propagate with the same velocity and without Separation. This direction is called the optic axis of the crystal. Any direction parallel to the optic axis is also an optic axis. Thus, an optic axis is direction a in the crystal and not a unique straight line passing through specific a set of points in the crystal. The optic axis is actually the axis of symmetry of the crystal. A ray of light propagating along the optic axis does not suffer double refraction, because the structure of the crystal is symmetrical about that direction.

What is Anisotropic material ?

Anisotropic Material- Material which exhibits double refraction phenomenon is known as anisotropic material. If the light is incident on a transparent anisotropic costal itis divided into two rays refracted with different velocities and in different directions.

What is Storege pool in data structure.

The storage pool contains all nodes that are not currently being used. This pool cannot be accessed by the programmer except through the getnode and feenode operations getnode removes a node from the pool whereas féénode returns a node to the pool. The most natural form for this pool to take is that of a linked list acting as a stack. The list is linked together by the new field in each node, The Remode operation removes the first node from this list and makes it available for use. The Renode operation adds a node to the front of the list, making it available for reallocation by the next getnode. The list of available nodes is called the available list.

Difference between an abstract data type specification and implementation

The abstract specification illustrates the role of an ADT as a purely logical definition of a new data type.
An ADT consist of two parts- a value defination and an operator defination. The value defination defines the collection of the value for the ADT and consist of two parts- a definition clause and a condition clause. Immediately following the value definition comes the operator definition. Each operator is defined as an abstract function with three parts - a header, the optional preconditions and the post conditions. The header specify any restrictions that must be setisfied before the operation can be applied. The post cordition specifies what the operation does.

Implementation-  an ADT means providing the procedure or production for each abstrct operation. The ADT instance are represented bt some concrete data struction that is manipulated by those procedure, according to the ADT's specification.

What is single processor implementation in data structure ?

Single Processor Implementation (Storage Areas)- When a subprogram is called in one processor, it must have a storage area; it must save the registers or whatevers else it will change, using the storage area also for its return address calling parameters, and local variables. As it returns, it will restore the registers and the other storage that it was expected to restore After the return it no longer needs anything in its local storage area.
In this way we implement subprogram calls by changing storage areas an action that takes the place of changing processors In these considerations it really makes no difference whether the subprogram is called recursively or not, providing that. in the recursive case, we are careful to regard two recursive calls as being different so that we do not mix the storage areas for me call with those ofanother, any more than we would mix storage areas for different subprograms one called from within the other.

What is digital circuit and system ?

A digital circuit is one in which the voltage levels assume a finite number of distinct values.
Digital circuits are often called switching circuits, because the voltage levels in a digital circuit are assumed to be switched from one value to another instantaneously, that is the transition time is assumed to be zero.
Digital circuits are also called logic circuits, because each type of digital circuit obeys a certain set of logic rules. The manner in which a logic circuit responds to an input is referred to the circuit's logic.
All of us are familiar with the impact of modern digital computers, communication systems, digital display systems, internet, e-mail, etc on society. One ofthe main of this revolution is the advent of integrated circuits (ICs ) which became possible because of the tremendous progress in emiconductor technology in recent years. Most of us may not be familiar ith the principles ofworking ofcomputers, communication systems, internet e-mail, etc. even though these have become an important part ofour daily life The operaton isbased m the ofthese sysems an many otersysems principles of digital techniques and these are referred to as digital systems.

Different source of water

we know that water is a main essential compound for living organism. The water which is used by living beings occurs from different sources of Water, basically there are two main sources of water which are follows-
1) Surface water--Water which is available from the earth surface is called surface water. It is generally clear and colourless and acidic in nature due to dissolved CO2 and organic matter. Surface water includes following types of water-

(a) Rain Water- Rainwater is obtained of evaporation from surface water, it is the purest form of natural water, during its downward Journey through the atmosphere it dissolved a considerable amount of industrial gases (like CO2 So2, No2 etc.) Rainwater is expensive to collect and irregular in supply.

(b) River Water- River water contain dissolved minerals like chlorides, sulphates bicarbonates of sodium magnesium, calcium and iron water from these sources now over the surface of land. The composition ofriver water not constant. In river water the greater is the amount of dissolved impurities. The amount of dissolved impurities depends on its contact of the soil.

(c) Lake Water-Lake water has more constant chemical composition. It has high quantity of organic matter but lesser amount of dissolved minerals. The chemical composition of lake water is constant.

(d) Sea Water- It is the most impure form of the natural water, because sea water contains various types of impurities. we know that all rivers join sea and throw in the impurities carried by them. There are many salts present in sea water. Bicarbonates of potassium magnesium and calcium and other harmful compounds  present in sea water.

2) Underground Water- Some part of rainwater which is reaches the inner surface of earth is called underground water mainly spring water and well water.
Generally spring and well water is clear in appearance due to the mering action of the soil, but this type of water contain moreover dissolved salts. Thus, water available from these sources contains high more hardness and organic impurities.