WHAT ARE REVERSIBLE AND IRREVERSIBLE PROCESSES

Reversible process -

A  Reversible process is that which can be retraced in opposite direction so that system and surrounding pass exactly through the same states as in the direct process .

If some work is done by the system in the direct process then same amount of work is done on the system  in the reverse process . Similarly , if some heat is absorbed by the system from the surrounding  in the direct process then same amount of heat energy is given back to the surrounding in the reverse process .

For a process to be reversible , it must satisfy the following conditions :

1. The process must be a very slow so that the system is always in state of mechanical and thermal equilibrium  . This system should be in chemical equilibrium  .
2. The system should be free from dissipative forces like friction , viscosity  etc .

Irreversible process -

A process which is not reversible i.e which can not be treated in opposite direction by taking it exactly through same states as attained in the direct process . Such a process followed by reverse process always leaves some change in the system or surrounding . 

Example - Conduction , diffusion  etc

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WHATB IS FERMI DIRAC STATISTICS

In the year 1926  , Fermi and  Dirac used the Pauli's exclusion principle to modify the BE STATISTICS  and successfully explained the behaviour of free electrons in metals . Thus , Fermi Dirac statistics came in to existence .
Following are the assumptions of FD statistics -

1. The particles of the system are indistinguishable and identical .
2. Available volume of phase space cell can not be less than h3 where h is Planck's constant 
3. A phase space cell can not contain more than one particle .
4. The number of  phase space cell is large as compared with the number of particles , such that occupation index  is less than or equals to one .
5. The particles of the system obey Pauli's exclusion principle

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WHAT ARE BOSONS

Definition -

Bosons are the particles of the system whose energy spectrum can be explained on the basis of BE statistics . Bosons do not obey Pauli's exclusion principle . That is two or more particles can exists in the same energy level . The bosons have integral spin -

Examples of bosons are as under :

1. Photons ( spin 1 )
2. K and π mesons ( spin 0 )
3. Atoms like helium , total spin of  whose electrons , protons and neutrons is integral .
4. Photons , that is quanta of light waves (spin 1 )

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WHAT IS BOSE EINSTEIN STATISTICS

Bose in the year 1924 , deduced the Planck's law of radiations on the basis of statistical considerations .

The basic assumptions of   Bose Einstein statistics  are -

• The particles of the system are indistinguishable and identical .
• Available volume of the phase space cell can not be less than h3 , where h is the Planck's constant .
• Any number of particles can  occupy a phase space cell .
• The number of phase space cell is comparable with the number of particles . that is occupation index is one .
• The particles of the system under consideration do not obey the Pauli's exclusion principle .

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WHAT IS BLACK HOLE

Definition of black hole -

A black hole is a region  of space from which gravity prevents anything from escaping . 

Event horizon -

 The boundary of region from which no escape is possibe  is called event horizon .     

   Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. In many ways a black hole acts like an ideal black body, as it reflects no light.Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a Kelvin for black holes of stellar mass, making it all but impossible to observe.

 Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.

 , the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbit can be used to determine its mass and location

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WHAT IS GREEN HOUSE EFFECT

DEFINITION -

 The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.



Green house  effect refers to circumstance where short wavelength of visible light from sun passes through a transparent medium and are absorbed  .

Solar radiation at the frequencies of visible light largely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.

If an ideal thermally conductive blackbody were the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30% of the incoming sunlight, this idealized planet's effective temperature (the temperature of a blackbody that would emit the same amount of radiation) would be about −18 °C. The surface temperature of this hypothetical planet is 33 °C below Earth's actual surface temperature of approximately 14 °C. The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere  .and is known as the greenhouse effect.
Earth’s natural greenhouse effect makes life as we know it possible. However, human activities, primarily the burning of fossil fuels and clearing of forests, have intensified the natural greenhouse effect, causing global warming .

Example of green house effect -

As bright sunlight warm our car on a cold ,clear day by green house effect

 

CONTRIBUTORS OF GREEN HOUSE EFFECT -

 Those gas molecules in the Earth's atmosphere with three or more atoms are called "greenhouse gases" because they can capture outgoing infrared energy from the Earth, thereby warming the planet. The greenhouse gases include water vapor with three atoms (H₂O), ozone (O₃), carbon dioxide (CO₂), and methane (CH₄). Also, trace quantities of chloro-fluoro-carbons (CFC's) can have a disproportionately large effect.

To attempt to quantify the effects of greenhouse gases on the global temperature, climatologists use the "radiative forcing" of the current atmospheric content of these gases.

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WHAT ARE BIODEGREDABLE PLASTICS

Definition -

Biodegradable plastics break down (degrade) upon exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion, and in some instances, rodent, pest, or insect attack are also included as forms of biodegradation or environmental degradation.
 Some modes of degradation require that the plastic be exposed at the surface, whereas other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present. Companies have made biodegradable additives to enhance the biodegradation of plastic

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WHAT ARE THERMOSETTING AND THERMOPLASTIS POLYMERS

There are two types of plastics:

•  thermoplastics

• thermosetting polymers.

THERMOPLASTICS -

 Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be molded again and again.
 Examples include polyethylene, polypropylene, polystyrene and polyvinyl chloride. Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units.

THERMOSETS -

Thermosets can melt and take shape once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Before heating with sulfur, the polyisoprene is a tacky, slightly runny material, but after vulcanization the product is rigid and non-tacky.

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WHAT IS ATMOSPHEREIC PRESSURE

Definition -

 Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface in the atmosphere of Earth (or that of another planet).

 In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. On a given plane, low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lb_f) (A column one square inch in cross-section would have a weight of about 14.7 lbs .

 SI UNIT OF PRESSURE -

  The Pascal unit is derived from Newton per meter-squared. However, the Newton is derived from kilogram meter per second-squared. Hence, by the use of base SI units only, the value of standard atmospheric pressure equals 101325 kg/( m s²), "kilogram per meter per second-squared".

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WHAT ARE TYPES OF FORCES

A force is a push or pull acting upon an object as a result of its interaction with another object. There are a variety of types of forces. A variety of force types were placed into two broad category headings on the basis of whether the force resulted from the contact or non-contact of the two interacting objects.

Contact Forces	Action-at-a-Distance Forces
Frictional Force	Gravitational Force
Tension Force	Electrical Force
Normal Force	Magnetic Force
Air Resistance Force
Applied Force
Spring Force

These types of individual forces will now be discussed in more detail.

• Applied Force
• Gravitational Force
• Normal Force
• Frictional Force
• Air Resistance Force
• Tension Force
• Spring Force

 

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WHAT IS FORCE OF FRICTION

Definition -

Friction is a force that is created whenever two surfaces move or try to move across each other. 

• Friction always opposes the motion or attempted motion of one surface across another surface.
• Friction is dependant on the texture of both surfaces.
• Friction is also dependant on the amount of contact force pushing the two surfaces together (normal force).

 The force of friction depends upon both surfaces in contact and the normal force.

there are two types of friction force - static friction and sliding friction. Sliding friction results when an object slides across a surface. As an example, consider pushing a box across a floor. The floor surface offers resistance to the movement of the box. We often say that the floor exerts a friction force upon the box. This is an example of a sliding friction force since it results from the sliding motion of the box. If a car slams on its brakes and skids to a stop (without antilock brakes), there is a sliding friction force exerted upon the car tires by the roadway surface. This friction force is also a sliding friction force because the car is sliding across the road surface. Sliding friction forces can be calculated from knowledge of the coefficient of friction and the normal force exerted upon the object by the surface it is sliding across. The formula is:
F_{frict-sliding} = μ_{frict-sliding} • F_norm
The symbol μ_{frict-sliding} represents the coefficient of sliding friction between the two surfaces. The coefficient value is dependent primarily upon the nature of the surfaces that are in contact with each other. For most surface combinations, the friction coefficients show little dependence upon other variables such as area of contact, temperature, etc. Values of μ_sliding have been experimentally determined for a variety of surface combinations and are often tabulated in technical manuals and handbooks. The values of μ provide a measure of the relative amount of adhesion or attraction of the two surfaces for each other. The more that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force.
Friction forces can also exist when the two surfaces are not sliding across each other. Such friction forces are referred to as static friction. Static friction results when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object. Suppose you were to push with 5-Newton of force on a large box to move it across the floor. The box might remain in place. A static friction force exists between the surfaces of the floor and the box to prevent the box from being set into motion. The static friction force balances the force that you exert on the box such that the stationary box remains at rest. When exerting 5 Newton of applied force on the box, the static friction force has a magnitude of 5 Newton. Suppose that you were to push with 25 Newton of force on the large box and the box were to still remain in place. Static friction now has a magnitude of 25 Newton. Then suppose that you were to increase the force to 26 Newton and the box finally budged from its resting position and was set into motion across the floor. The box-floor surfaces were able to provide up to 25 Newton of static friction force to match your applied force. Yet the two surfaces were not able to provide 26 Newton of static friction force. The amount of static friction resulting from the adhesion of any two surfaces has an upper limit. In this case, the static friction force spans the range from 0 Newton (if there is no force upon the box) to 25 Newton (if you push on the box with 25 Newton of force). This relationship is often expressed as follows:
F_frict-static ≤ μ_frict-static• F_norm
The symbol μ_frict-static represents the coefficient of static friction between the two surfaces. Like the coefficient of sliding friction, this coefficient is dependent upon the types of surfaces that are attempting to move across each other. In general, values of static friction coefficients are greater than the values of sliding friction coefficients for the same two surfaces. Thus, it typically takes more force to budge an object into motion than it does to maintain the motion once it has been started.
 

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WHAT IS KINETIC ENERGY

Kinetic energy is the energy which that moving objects have.
 Kinetic energy is  the energy of movement, because it refers to any object that is moving at that present time. This energy can be changed into other sorts of energy such as heat (if something hits with something soft and does not bounce), potential energy (if it is moving upwards and gets higher), or even light .However, heat, light, sound, mechanical energy, electrical, and other types of energy are also types of kinetic energy.
Kinetic Energy is equal to the mass of something times its velocity (or speed) times its velocity again, all times ½:

Meteors, bullets from a gun, a kicked football and all other moving objects have kinetic energy.

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WHAT ARE THE TYPES OF THERMODYNAMIC EQUILIBRIUM

Definition -

When a system interacting with its surrounding stops exchange of energy and matter with its surrounding , it is called in the state of thermodynamic equilibrium . 

TYPES OF THERMODYNAMIC EQUILIBRIUM -

There  are many types of thermodynamic equilibrium -

• Mechanical equilibrium
• Thermal equilibrium
• Chemical equilibrium etc

Mechanical equilibrium -

A state of mechanical equilibrium is that state in which it experience no pressure or elastic stress within it and there is no unbalanced force between the system and surrounding  . 

Thermal equilibrium -

In the state of thermal equilibrium of the system , there is no exchange of heat energy between the system and surrounding  . Such a state is characterized by same value of the temperature of the system and surrounding .

Chemical equilibrium -

In the state of chemical equilibrium system does not undergo a spontaneous change in its internal composition  i.e no chemical  reaction takes place in it and no transfer of matter takes place from one

part  of it to another part .

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WHAT ARE APPLICATIONS OF REMOTE SENSING

There are lot of applications of remote sensing , which can be discussed as -

• Conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Doppler radar is used by local law enforcements’ monitoring of speed limits and in enhanced meteorological collection such as wind speed and direction within weather systems in addition to precipitation location and intensity. Other types of active collection includes plasmas in the ionosphere. Interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain (See RADARSAT, TerraSAR-X, Magellan).

• Laser and radar altimeters on satellites have provided a wide range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so. By measuring the height and wavelength of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions.
• Light detection and ranging (LIDAR) is well known in examples of weapon ranging, laser illuminated homing of projectiles. LIDAR is used to detect and measure the concentration of various chemicals in the atmosphere, while airborne LIDAR can be used to measure heights of objects and features on the ground more accurately than with radar technology. Vegetation remote sensing is a principal application of LIDAR.
• Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a wide range of frequencies. The most common are visible and infrared sensors, followed by microwave, gamma ray and rarely, ultraviolet. They may also be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere.
• Stereographic pairs of aerial photographs have often been used to make topographic maps by imagery and terrain analysts in trafficability and highway departments for potential routes.
• Simultaneous multi-spectral platforms such as Landsat have been in use since the 70’s. These thematic mappers take images in multiple wavelengths of electro-magnetic radiation (multi-spectral) and are usually found on Earth observation satellites, including (for example) the Landsat program or the IKONOS satellite. Maps of land cover and land use from thematic mapping can be used to prospect for minerals, detect or monitor land usage, deforestation, and examine the health of indigenous plants and crops, including entire farming regions or forests. Landsat images are used by regulatory agencies such as KYDOW to indicate water quality parameters including Secchi depth, chlorophyll a density and total phosphorus content. Weather satellites are used in meteorology and climatology.
• Hyperspectral imaging produces an image where each pixel has full spectral information with imaging narrow spectral bands over a contiguous spectral range. Hyperspectral imagers are used in various applications including mineralogy, biology, defence, and environmental measurements.
• Within the scope of the combat against desertification, remote sensing allows to follow-up and monitor risk areas in the long term, to determine desertification factors, to support decision-makers in defining relevant measures of environmental management, and to assess their impacts.

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WHAT ARE EIGEN VALUES AND EIGEN FUNCTIONS

The wavefunction for a given physical system contains the measurable information about the system. To obtain specific values for physical parameters, for example energy, you operate on the wavefunction with the quantum mechanical operator associated with that parameter. The operator associated with energy is the Hamiltonian, and the operation on the wavefunction is the Schrodinger equation. Solutions exist for the time independent Schrodinger equation only for certain values of energy, and these values are called "eigenvalues*" of energy.
Corresponding to each eigenvalue is an "eigenfunction*". The solution to the Schrodinger equation for a given energy involves also finding the specific function which describes that energy state. The solution of the time independent Schrodinger equation takes the form
The eigenvalue concept is not limited to energy. When applied to a general operator Q, it can take the form
if the function is an eigenfunction for that operator. The eigenvalues qi may be discrete, and in such cases we can say that the physical variable is "quantized" and that the index i plays the role of a "quantum number" which characterizes that state.

Energy eigenvalues

*"Eigenvalue" comes from the German "Eigenwert" which means proper or characteristic value. "Eigenfunction" is from "Eigenfunktion" meaning "proper or characteristic function".

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WHAT IS SPECIFIC HEAT OF SOLIDS

Definition -

Specific heat of solids is the measure of the number of degrees of freedom .

       The specific heat of a substance is defined as the heat energy absorbed by one unit mass of the substance to raise its temperature by one degree . 

 While   measuring the specific heat either volume or pressure is kept constant . But in case of solids , we usually speak of the specific heat at constant volume and is given as -

             Cv =( ∂Q/ ∂T)v = (∂E+P ∂V)/dT =( ∂E/ ∂T)v

Partial  derivative is taken since E may be the function of other quantities , subscript v shows that volume is kept constant .

Whenever  energy  is added  to a solid , the increase in its energy occurs in two ways , firstly the energy is used to vibrate the lattice very vigorously and secondly the free electrons in the metals and semiconductors may be excited to higher energy levels . Therefore ,

C(solid )= C(lattice) + C (electronic )

The  electronic contribution  to specific heat is very small at room temperature and hence we speak  of  only the specific  heat by lattice only

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WHAT IS AIR RESISTANCE

Definition -

Air resistance, also called drag, is the forces that are in opposition to the relative motion of an object through the air.
 Drag forces act opposite to the oncoming flow velocity. Drag, unlike other resistive forces, depends directly on velocity. Drag is the component of the net aerodynamic force acting opposite to the direction of the movement and the forces working perpendicular are called lift. Drag is overcome by thrust. In astrodynamics, atmospheric drag is both a positive and a negative force depending on the situation. It is a drain on fuel and efficiency during lift-off and a fuel savings when a spacecraft is returning from to Earth.
Air resistance is usually calculated using the drag equation. This equation calculates the force experienced by an object moving through a fluid or gas at relatively large velocity. The result is called quadratic drag.

 Types of drags -

There are three main types of drag in aerodynamics: lift induced, parasitic, and wave.

 Each affects an objects ability to stay aloft as well as the power and fuel needed to keep it there.

Lift induced -

Lift induced(induced)drag occurs as the result of the creation of lift on a three-dimensional lifting body.

Parasitic drag -

 Parasitic drag is caused by moving a solid object through a fluid. Parasitic drag is made up of multiple components including form drag and skin friction drag.

Wave drag -

 Wave drag (compressibility drag) is created by the presence of a body moving at high speed through a compressible fluid.
 In aerodynamics, wave drag consists of multiple components depending on the speed regime of the flight. In transonic flight (Mach 0.5 but less than 1.0), wave drag is the result of local supersonic flow are created.

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WHAT IS INERTIA

Definition -

Inertia is the resistance of an object to any change in its motion, including a change in direction. An object will stay still or keep moving at the same speed and in a straight line, unless it is acted upon by an outside force.

Example of inertia -

For example, a rubber ball will not start bouncing around unless someone picks it up and throws it. Basically, if an object is not moving, it won't start moving unless something else acts upon it. The same idea can be applied to motion: an object in motion will stay in motion unless some outside, opposing force acts upon it. Inertia is also called Sir Isaac Newton's First Law of Motion.
The First Law of Motion says that:

Every body perseveres in its state of being at rest or of moving uniformly straight ahead, except insofar as it is compelled to change its state by forces impressed.
or
Every object stays at rest or stays moving at the same speed unless something makes it change. 

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WHAT IS STRUCTURE OF GRAPHENE

Definition-

Graphene is the form of carbon . Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. It is remarkably strong for its very low weight (100 times stronger than steel) and it conducts heat and electricity with great efficiency.

Structure of graphene -

graphene is a crystalline allotrope of carbon with 2-dimensional properties. In graphene, carbon atoms are densely packed in a regular sp²-bonded atomic-scale chicken wire (hexagonal) pattern. Graphene can be described as a one-atom thick layer of graphite. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons.

Graphene's stability is due to a tightly packed, periodic array of carbon atoms and an sp2 orbital hybridization - a combination of orbitals p_x and p_y that constitute the σ-bond. Graphene has three σ-bonds and one π-bond. The final p_z electron makes up the π-bond, and is key to the half-filled band that permits free-moving electrons.
Graphene sheets in solid form usually show evidence in diffraction for graphite's (002) layering. This is true of some single-walled nanostructures. However, unlayered graphene with only (hk0) rings has been found in the core of presolar graphite onions. TEM studies show faceting at defects in flat graphene sheets and suggest a role for two-dimensional crystallization from a melt.

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MATHEMATICAL DESCRIPTION AND UNIT OF FORCE

Definition -

Force is that push or pull which change the position of an object from one position to the other position .

 A force is any influence which tends to change the motion of an object. In other words, a force can cause an object with mass to change its velocity  i.e., to accelerate. Force can also be described by intuitive concepts such as a push or a pull. A force has both magnitude and direction, making it a vector quantity.

Unit of force-

 It is measured in the SI unit of newtons and represented by the symbol F.

Mathematical description -

The original form of Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. As a formula, this is expressed as:

where the arrows imply a vector quantity possessing both magnitude and direction.
Related concepts to force include: thrust, which increases the velocity of an object; drag, which decreases the velocity of an object; and torque which produces changes in rotational speed of an object. In an extended body, each part usually applies forces on the adjacent parts; the distribution of such forces through the body is the so-called mechanical stress. Pressure is a simple type of stress. Stress usually causes deformation of solid materials, or flow in fluids.

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