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.

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.

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.

Explain liquid drop model of atomic nucleus.

Explain liquid drop model of atomic nucleus.
Explanation-
According to this model a necleus can be assumed to be like a liquid drop for the following reasons-
(i) The stable necleus is spherical in shape due to symmetrical surface tension forces.
(ii) Such as the surface tension forces act on thevsurface of the liquid-drop similarly a potential barrier to surface of the nucleus acts.
(iii) The nuclear force are short range forces. Similarly, in liquid drop, the intermolecular forces are short range forces.
(iv) The density of liquid drop is independent of its volume. Similarly the density of nucleus is independent of its volume.
(v) On rising the temprature of liquid the molecules evaporate. Similarly, when energy is given to the neucleus a compound nucleus is formed which emits nucleons almost immediately . 

History of superconductivity

Superconductivity is a state exhibited by many conductors when cooled below their superconductivity transition temperature. Superconductivity is one of the most fascinating physical phenomena having a vast potentiality in practical application. A superconductor 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.   

What is a LASER ?

The word LASER is the short of light amplification by stimulated emission of radiation. Laser is that device is which an intense, monochromatic, coherent and uni-directional light beam is obtained. It was discovered in 1950, by Townes and Shallow.
Thus, a Laser produces a light beam in which all the waves are of same frequency.  all waves are in same phase and all waves travel in a definite direction

What is Newton's Rings

When a Plano-convex lens with its convex surface is placed on a plane glass plate, an air film gradually increasing thickness is formed between the two. The thickness of the film at the point of contact is zero. If monochromatic light is allowed to fall normally, and the film is viewed in reflected light , alternate dark and bright concentric rings with their center dark is formed between the lens and glass plate are seen. Since the phenomenon was described by Newton that is way the rings are known as Newton's Rings after his name.

Explain the Interference of Light.

When two light waves superimpose, then the resultant amplitude ( or intensity ) in the region of superposition is different then the amplitude of individual waves. this modification in distribution of intensity in the region of superposition is called inerteference. 
When the resultant amplitude is the sum of the amplitudes due to two waves, the interference is known as constructive interference and when the resultant amplitude is equal to the difference of two amplitude, the interference is known as destructive interference.


Types of interference-
i) Division of Wavefront
ii)Division of Amplitude

What is core type transformer ?

Constructionally there are rwo types of transformers i.e. Core type transformer and Shell type transformer. There are differ from each other by the manner in which the winding are wound around the magnetic core.
Core type transformer- in Core type transformers , the windings surround a considerable part of the core, i.e. The half turns of primary and secondary windings are placed on each limb (core).
Generally, circular coils are used in core transformer because of their mechanical strengh. Such cylindrical coil are wound in helical layer with the different layers insulated from each other by paper, cloth, micarta board or cooling ducts. Figure shows the diagram of Core type transformer.

What is Compton Effect?

In 1921, Professor A.H. Compton discovered that whrn a mono-chrometic beam of light of high frequency radiation ( X-rays, Y-rays, etc.) is scattered by a substance, the scattered radiation contain two components
-One having a lower frequency or greater wavelength and the another having the same frequency or wavelength.
The radiation of of unchanged frequency in the scattered beam is knows as unmodified radiation while the radiation of lower frequency is called as modified radiation.
And the difference in wavelength is known as Compton Effect.

Zener breakdown

ZENER BREAKDOWN
In this case breakdown occurs in junctiins, which are heavily doped. When the reverse voltage is increased , the electric field at the junction also increses. A strong electric field causes a covelent bond to break from the crystal structure. As a result a large number of minority carriers are generated and a large current flows though the junction.

What are intrinsic and extrinsic semiconductors ?

The semiconductors are of mainly two types-

(i) intrinsic semiconductor - A semiconductor, which is in its extremely pure form , is known as an intrinsic (or pure) semiconductor. The nature of semiconductors is such that even a small amount of certain impurities can change their electrical properties drastically. It is due to this fact, that a semiconductor would not be called truly intrinsic, unless the impurity level is very small .
The silicon and germanium are two most widely used intrinsic semiconductors.

(i) Extrinsic semiconductors- When a small quantity of impurity is mixed in a pure or intrinsic semiconductor is called the extrinsic semiconductors. The conductivity of resultant crystal depends on the nature and quantity of the impurity added . Depending upon the nature of impurity added in intrinsic semiconductor.
The extrinsic semiconductor are of two types-
    (a) N- type or doner
    (a) P- type or acceptor.

What is semiconductor ?

The materials, whose electrical properties lie between those of conductors and insulators, are know as semiconductor.
The exampels of such materials are-
»cadmium sulphides(CdS),
«gremanium(Ge),
»silicon(Si),
«gallium arsenide(GaAs),
»lead telluride  etc

In terms of energy bands , the semiconductors may be defined as those materials, which at room temperature, have

(i) Partial filled conduction band
(ii)Partial filled valenced band

In semiconductor, at absolute zero temperature there are no electrons in the conduction band and the valence band is completely filled. Thus semiconductors behaves like perfect insulators at 0°K.
However, as the temperature increased, the width of energy gap reduces. Consequently, some of the electrons jump into conduction band and semiconductor show some conductivity. It is thus obvious, that the conductivity of semiconductor increase in temprature.