QUANTUM MECHANICS

Prepared by:

MUHAMMAD REHAN ASGHAR

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Quantum Mechanics

Definition:

Quantum mechanics (QM – also known as quantum physics, or quantum theory) is a branch of physics which deals with physical phenomena at microscopic scales, where the action is on the order of the Planck constant. It departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales. Quantum mechanics provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It is the non-relativistic limit of quantum field theory (QFT), a theory that was developed later that combined quantum mechanics with relativity.

Origin:

Scientific inquiry into the wave nature of light began in the 17th and 18th centuries when scientists proposed a wave theory of light based on experimental observations.

PRE – 1900:In 1803, Thomas Young, performed the

famous double-slit experiment that he later described in a paper entitled "On the nature of light and colors". This experiment played a major role in the general acceptance of the wave theory of light.

In 1838, with the discovery of cathode rays by Michael Faraday, these studies were followed by the statement of Gustav Kirchhoff about the black-body radiation , later in 1877 it is suggested by  Boltzmann that the energy states of a physical system can be discrete, and the 1900 quantum hypothesis of Max Planck. Planck's hypothesis that energy is radiated and absorbed in discrete "quanta" (or "energy elements") precisely matched the observed patterns of black-body radiation..

Among the first to study quantum phenomena in nature were:

 Compton  Pieter Zeeman

Each of them has a quantum effect named after him.

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DOUBLE - SLIT EXPERIMENT

Millikan studied the Photoelectric effect experimentally and Albert Einstein developed a

theory for it. At the same time

Niel Bohr developed his theory of the atomic structure.

According to Planck, each energy element E is proportional to

Its frequency v: E = hv

Where, h is Planck's constant. Planck insisted that this was simply an aspect of the processes of absorption and emission of radiation and had nothing to do with the physical reality of the radiation itself. In fact, he considered his quantum hypothesis a mathematical trick to get the right answer rather than a sizeable discovery. However, in 1905 Albert Einstein interpreted Planck's quantum hypothesis realistically and used it to explain the photoelectric effect, in which shining light on certain materials can eject electrons from the material.

POST – 1900:The foundations of quantum mechanics were established during

the first half of the 20th century by Max Planck, Niels Bohr, Heisenberg, Louis de Broglie, Arthur Compton, Albert Einstein,  Schrödinger, Sommerfeld and others. In the mid-1920s, developments in quantum mechanics led to its becoming the standard formulation for atomic physics. In the summer of 1925, Bohr and Heisenberg published results that closed the "Old Quantum Theory". Out of deference to their particle-like behavior in certain processes and measurements, light quanta came to be called photons (1926). From Einstein's simple postulation was born a flurry of debating, theorizing, and testing. Thus the entire field of quantum physics emerged.

Electromagnetic Waves:The other exemplar that led to quantum

mechanics was the study of electromagnetic waves, such as visible and ultraviolet light. When it was found in 1900 by Max Planck that the energy of waves could be described as consisting of small packets or "quanta", Albert Einstein further developed this idea to show that an electromagnetic wave such as light could also be described as a particle (later called the photon) with a discrete quantum of energy that was dependent on its frequency. As a matter of fact, Einstein was able to use the photon theory of light to explain the photoelectric effect, for which he won the Nobel Prize in 1921. This led to a theory of unity between subatomic particles and electromagnetic waves, called wave–particle

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BOHR'S ATOMIC MODEL

MAX PLANCK is considered as a father of Quantum

Mechanics.

duality, in which particles and waves were neither one nor the other, but had certain properties of both. Thus coined the term wave-particle duality.

While quantum mechanics traditionally described the world of the very small, it is also needed to explain certain recently investigated macroscopic systems such as superconductors, superfluids, and larger organic molecules.

Quantum:The word “quantum” derives from

the Latin, meaning "how great" or "how much". In quantum mechanics, it refers to a discrete unit that quantum theory assigns to certain physical quantities, such as the energy of an atom at rest. The discovery that particles are discrete packets of energy with wave-like properties led to the branch of physics dealing with atomic and sub-atomic systems which is today called quantum mechanics. It is the underlying mathematical framework of many fields of physics and chemistry, including condensed matter physics, solid-state physics, atomic physics, molecular physics, computational physics, computational chemistry, quantum chemistry, particle physics, nuclear chemistry, and nuclear physics.

Failure Of Classical Mechanics:If Classical mechanics alone governed the workings of an atom, electrons could not really

"orbit" the nucleus. Since bodies in circular motion are accelerating, electrons must emit radiation, losing energy and eventually colliding with the nucleus in the process. This clearly contradicts the existence of stable atoms. However, in the natural world, electrons normally remain in an uncertain, non-deterministic, "smeared", wave–particle wave function orbital path around (or through) the nucleus, defying the traditional assumptions of classical mechanics and electromagnetism.

Basic Purpose of Quantum Mechanics:

Quantum mechanics was initially developed to provide a better explanation and description of the atom, especially the differences in the spectra of light emitted by different isotopes of the same element, as well as subatomic particles. In short, the quantum-mechanical atomic model has succeeded spectacularly where classical mechanics and electromagnetism falter.Broadly speaking, quantum mechanics incorporates four classes of phenomena for which classical physics cannot account:

Quantization of Certain Physical properties. Wave – Particle duality.

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DIAGRAM OF A QUANTUM

The uncertainty principle. Quantum entanglement.

Working Principle:

The Principles of Quantum Mechanics was first published by Oxford University Press in 1930.Dirac gives an account of quantum mechanics by "demonstrating how to construct a completely new theoretical framework from scratch"; "problems were tackled top-down, by working on the great principles, with the details left to look after themselves". It leaves classical physics behind after the first chapter presenting the subject with a logical structure. Its 82 sections contain 785 equations with no diagrams.

Role of Quantum Mechanics In Future:

The strange behavior of quantum physics might seem too unpredictable to rely on for our energy needs, but new technologies hope to capitalize on its very strangeness. The most familiar of these quantum tricks is the fact that light acts both like a wave and a particle.

This dual nature is utilized in solar power technology. Incoming sunlight is concentrated by mirrors and lenses that rely on the wave-like properties of light. Once inside a solar cell, however, this focused light collides with electrons in a particle-like way, thus freeing the electrons to create an electric current.

Quantum dots:

The next generation of solar cells may employ tiny bits of semiconductor material called quantum dots. These nanometer-sized devices are so small that only a handful (anywhere from 1 to 1,000) of free electrons can reside inside.

Because of these cramped quarters, a quantum dot behaves like an artificial atom in that its electrons can reside only at specific (so-called quantized) energy levels. These levels define exactly what wavelengths of light the dot will absorb.

Some of researchers are looking to tune the wavelengths at which a dot absorbs light by making it bigger or smaller. Solar cell manufacturers may one day be able to mix together dots of different sizes to absorb sunlight along a wide range of wavelengths.

Quantum wires:

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QUANTUM DOTS

A quantum wire is like a quantum dot stretched out along one direction. In certain cases, this narrow conduit — 10,000 times thinner than a human hair — can be very good at conducting electricity, as the electrons tend to move in a more orderly fashion down the wire.

One way to make quantum wires is with carbon nanotubes, which are small rolled-up sheets of hexagonally-bound carbon. It was discovered that these nanotubes are beginning to show up in all types of applications, including better energy storage.

As one MIT group has shown, it is possible to make a souped - up capacitor from carbon nanotubes. The researchers grow the nanotubes close together — in what is likely the world's tiniest carpet — to increase surface area inside the capacitor.

The resulting "ultra-capacitor" could store as much as 50 percent of the electricity that a similarly-sized battery can, the scientists claim. This might be ideal inside an electric car, as capacitors are more durable and can charge and discharge much faster than batteries.

Superconductors:

Although quantum wires can be good conductors, another quantum substance is the best. Superconductors are materials in which the electrons pair up to carry the current. This pairing is unusual because electrons typically repel each other, but quantum physics overcomes this and, in so doing, reduces the electrical resistance in the superconductor to zero.

Resistance is what makes a wire get hot when it carries electricity. Power companies typically lose about 7 percent of their energy to heat caused by resistance in transmission wires.

Superconducting wires could help reduce this waste. The trouble is that superconductors only work at extremely cold temperatures.

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QUANTUM WIRES

This photo shows a magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen.

For example, the longest superconducting cable system for transmitting power — installed earlier this year along a half-mile stretch of the Long Island power grid by American Superconductor Corporation and its partners — must be surrounded by liquid nitrogen to keep it at minus 330 degrees Fahrenheit (minus 200 degrees Celsius).American Superconductor is also working on applying its superconducting wires to offshore wind turbines, in order to make them smaller and more efficient.

Light-emitting diodes:

One good way to use all this quantum-derived electricity is to turn on a light-emitting diode, or LED, which works like a solar cell but in reverse.

Electric current going through the diode causes electrons to jump across a barrier between two types of semiconductor material. The jumping electrons then fall into lower energy states, emitting a photon. Because the wavelength of this emitted light is in a very narrow band, there is not a lot of wasted energy emitted in the infrared, as is the case for normal incandescent light bulbs. An LED's efficiency is even better than that of compact fluorescents.

LEDs are now being made into full light fixtures that can replace normal bulbs. Their extra cost can be offset by lower electricity bills.

In the energy saving business, every quantum bit can help.

The Strangest Little Things in Nature Forget Crystal Balls: Let the Power of Math Inform Your Future Innovations: Ideas and Technologies of the Future.

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LE.D. LIGHTS

CONCLUSION

In regard of all of the above Scientists, Experiments, statements & Laws, we can conclude that without any doubt Quantum Mechanics proved so much helpful on Microscopic Level as Old Mechanics was not able to define that phenomenon’s.

There was a time when scientists thought that now it is the end of Physics or Mechanics & they have discovered all of the phenomenon’s but when they started work on Microscopic Level then a whole new branch of physics arose called “ Quantum Mechanics “.

Quantum Mechanics enables us to understand many of the atomic or microscopic phenomenon’s such as:

Structure and behavior of Atom. Chemistry of atom. Stability of matter. Behavior of light ( Interferences , photons …) Behavior of matter ( Conductivity , Super – Conductivity , Heat Capacity …) Electronics Sub – atomic Constituents Anti – matter

These above things were successfully explained through Quantum Mechanics. It proves so much useful to mankind and will prove. Now a days, Scientists are doing a lot of researches on different phenomenon’s of Quantum Mechanics and they are hope so that they will produce extra – ordinary products in future which will change our thinking and our views about Quantum Mechanics.

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REFERENCES

Definition:

http://en.wikipedia.org/wiki/Quantum_mechanics

Origin:

http://en.wikipedia.org/wiki/Quantum_mechanics

Working Principles:

http://en.wikipedia.org/wiki/The_Principles_of_Quantum_Mechanics

Future Prospects :

http://www.livescience.com/7547-quantum-physics-power-future.html

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