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...
Friday, 8 August 2014
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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 -
The particles of the system are indistinguishable and identical .
Available volume of phase space cell can not be less than h3 where h is Planck's constant
A phase space cell can not contain more than one particle .
The number of ...
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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 :
Photons ( spin 1 )
K and π mesons ( spin 0 )
Atoms like helium , total spin of whose electrons , protons and neutrons is integral .
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...
Thursday, 7 August 2014
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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...
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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...
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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...
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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...
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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
...
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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...
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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...
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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,...
Wednesday, 6 August 2014
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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...
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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...
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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...
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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 -
...
Tuesday, 5 August 2014
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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...
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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...
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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...
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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...
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WHAT IS ACCELERATION
Definition-
Acceleration, in physics, is the rate at which the velocity of an object changes over time.
An object's acceleration is the net result of any and all forces acting on the object, as described by Newton's Second Law.
SI unit of acceleration -
The SI unit for acceleration is the metre per second squared (m/s2).
Accelerations are vector quantities (they have magnitude and direction) and add according to...
Monday, 4 August 2014
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WHAT IS THERMODYNAMICS
Definition-
Thermodynamics is a branch of physics concerned with heat and temperature and their relation to energy and work.
It defines macroscopic variables, such as internal energy, entropy, and pressure,
that partly describe a body of matter or radiation. It states that the
behavior of those variables is subject to general constraints, that are
common to all materials, not the peculiar properties of particular
materials. These general constraints are expressed in the four laws of
thermodynamics. Thermodynamics...
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DUAL NATURE OF MATTER : DE BROGLIE WAVELENGTH
Definition
The dual characteristics property of matter is called dual nature of light .
The phenomena like interference , diffraction and polarisation of light were experimentally known and indicate that light is of wave nature . On the other hand ,photoelectric effect and Compton effect illustrate the particle nature , i.e. electromagnetic radiation or light is of particle nature .
de - Broglie hypothesis -
According to de -Broglie hypothesis , the dual nature should not confined to radiation but should...
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WHAT IS MODERN PHYSICS
Description of modern physics -
The term modern physics refers to the post-Newtonian conception of physics. Modern physics deals with the underlying structure of the smallest particles in nature as well as a rigorous understanding of the fundamental interaction of particles, understood as forces. Small velocities and large distances is usually the realm of classical physics.
Modern physics often involves extreme conditions; quantum effects usually involve distances comparable to atoms (roughly 10−9 m),...
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WHAT ARE PARTICLE AND NUCLEAR PHYSICS
Particle physics
Particle physics is a branch of physics which studies the nature of particles that are the constituents of what is usually referred to as matter and radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics. Although the word "particle" can be used in reference to many objects (e.g. a proton,
a gas particle, or even household dust), the term "particle physics"
usually refers to the study of "smallest" particles and the fundamental...
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WHAT IS CONDENSED MATTER PHYSICS
Definition
Condensed matter physics is a branch of physics that deals with the physical properties of condensed phases of matter. Condensed matter physicists seek to understand the behavior of these phases by using physical laws. In particular, these include the laws of quantum mechanics, electromagnetism and statistical mechanics.
Condensed matter physics is
the field of physics that deals with the macroscopic physical properties
of matter. In particular, it is concerned with the "condensed" phases
that...
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WHAT IS APPLIED PHYSICS
Definition
Applied physics is physics which is intended for a particular technological or practical use. It is usually considered as a bridge or a connection between "pure" physics and engineering.
Applied
physics is a general term for physics research which is intended for a
particular use. An applied physics curriculum usually contains a few
classes in an applied discipline, like geology or electrical
engineering. It usually differs from engineering
in that an applied physicist may not be designing something...
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WHAT IS ASTROPHYSICS
Astrophysics
Astrophysics
and astronomy are the application of the theories and methods of
physics to the study of stellar structure, stellar evolution, the origin
of the solar system, and related problems of cosmology.
Because astrophysics is a broad subject, astrophysicists typically
apply many disciplines of physics, including mechanics,
electromagnetism, statistical mechanics, thermodynamics, quantum
mechanics, relativity, nuclear and particle physics, and atomic and
molecular physics.
The discovery by Karl...
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WHAT ARE ATOMIC AND MOLECULAR PHYSICS
Atomic, molecular, and optical physics
Atomic,
molecular, and optical physics (AMO) is the study of matter–matter and
light–matter interactions on the scale of single atoms
and molecules. The three areas are grouped together because of their
interrelationships, the similarity of methods used, and the commonality
of their relevant energy scales. All three areas include both classical,
semi-classical and quantum treatments; they can treat their subject
from a microscopic view (in contrast to a macroscopic view).
Atomic...
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WHAT ARE CUBIC CRYSTALS
Definition - centred cubic crystals
A cubic crystal is a crystal system in which unit cell is a cube . There are three types of cubic crystals .
These are -
Simple cubic crystals . (s.c )
Face centred cubic or cubic closed packed crystals . (fcc )
Body centred cubic crystals .( bcc )
These terms can be explained as -
Simple cubic crystals -
In this structure , the unit cell has atoms only at...
Friday, 1 August 2014
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WHAT IS PHYSICS
DEFINITION -
Physics is the natural science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.
Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches of mathematics, and biology, but...
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USES OF X RAYS
X-ray crystallography in which the pattern produced by the diffraction
of X-rays through the closely spaced lattice of atoms in a crystal is
recorded and then analysed to reveal the nature .
X-ray astronomy, which is an observational branch of astronomy, which deals with the study of X-ray emission from celestial objects.
X-ray microscopic analysis, which uses electromagnetic radiation in the soft X-ray band to produce images of very small objects.
X-ray fluorescence,
a technique in which X-rays are generated within a...
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PROPERTIES OF X -RAYS
X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a short amount of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer.
In medical imaging this increased cancer risk is generally greatly
outweighed by the benefits of the examination. The...
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WHAT ARE X -RAYS
X-radiation (composed of X-rays) is a form of electromagnetic radiation. Most X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays.
X-radiation is also referred to with terms meaning Röntgen radiation, after Wilhelm Röntgen, who is usually credited as its discoverer,...
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SOURCES OF COSMIC RAYS
cosmic rays originating from supernovae. A 1948 proposal by Horace W. Babcock suggested that magnetic variable stars could be a source of cosmic rays. Crab Nebula is also considered as a source of cosmic rays. Since then, a wide variety of potential sources for cosmic rays began to surface, including supernovae, active galactic nuclei, quasars, and gamma-ray bursts.
In 2009, supernovae were said to have been "pinned down"...
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WHAT ARE COSMIC RAYS
Cosmic rays are immensely high-energy radiation, mainly originating outside the Solar System. They may produce showers of secondary particles that penetrate and impact the Earth's atmosphere and sometimes even reach the surface. Composed primarily of high-energy protons and atomic nuclei, they are of mysterious origin. Active galactic nuclei probably also produce cosmic rays.
The term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation. In common scientific...
Thursday, 31 July 2014
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WHAT IS ESCAPE VELOCITY
escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero.
It is the speed needed to "break free" from the gravitational
attraction of a massive body, without further propulsion, i.e., without
spending more fuel.
For a spherically symmetric body, the escape velocity at a given distance is calculated by the formula
where G is the universal gravitational constant (G = 6.67×10−11 m3 kg−1 s−2),...
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WHAT IS ENERGY
Energy is the capacity of a body to do work .
energy is a property of objects, transferable among them via fundamental interactions, which can be converted in form but not created or destroyed. The joule is the SI unit of energy, based on the amount transferred to an object by the mechanical work of moving it 1 metre against a force of 1 newton.
Work and heat are two categories of processes or mechanisms that can transfer a given amount of energy.
The second law of thermodynamics limits the amount of work that can be performed...
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WHAT IS VELOCITY
Velocity is the rate of change of the position of an object, equivalent to a specification of its speed and direction of motion, e.g. 60 km/h to the north. Velocity is an important concept in kinematics, the branch of classical mechanics which describes the motion of bodies.
Velocity is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value (magnitude) of velocity is called "speed",...
