Download Basic Purpose of Quantum Mechanics

QUANTUM
MECHANICS
Prepared by:
MUHAMMAD REHAN ASGHAR
1
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
DOUBLE - SLIT EXPERIMENT
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.
2
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
BOHR'S ATOMIC MODEL
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 MAX PLANCK is considered as a
father of Quantum Mechanics.
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
3
which he won the Nobel Prize in 1921. This led to a theory of unity between subatomic
particles and electromagnetic waves, called wave–particle duality, in which particles and waves
were neither one nor the other, but had certain properties of both. Thus coined the term waveparticle 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, solidDIAGRAM OF A QUANTUM
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:
4




Quantization of Certain Physical properties.
Wave – Particle duality.
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.
5
QUANTUM DOTS
Quantum wires:
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.
QUANTUM WIRES
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 similarlysized 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.
This photo shows a magnet levitating above a high-temperature
Resistance is what makes a wire get hot
superconductor, cooled with liquid nitrogen.
when it carries electricity. Power
companies typically lose about 7 percent of their energy to heat caused by resistance in
transmission wires.
6
Superconducting wires could help reduce this waste. The trouble is that superconductors only work
at extremely cold temperatures.
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 quantumderived 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
LE.D. LIGHTS
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.
7
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.
8
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
9