Diffraction Diffraction pattern of red laser beam made on a plate after passing a small circular hole in another plate Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays and radio waves. Richard Feynman[3] wrote: The formalism of diffraction can also describe the way in which waves of finite extent propagate in free space. Examples[edit] History[edit] where
File:Atom diagram.png Electromagnetic radiation The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The two types of fields in EMR waves are always in phase with each other with a fixed ratio of electric to magnetic field intensity. Electromagnetic radiation (EM radiation or EMR) is a form of radiant energy, propagating through space via electromagnetic waves and/or particles called photons. In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. EMR carries energy—sometimes called radiant energy—through space continuously away from the source (this is not true of the near-field part of the EM field). Physics[edit] Theory[edit] Maxwell’s equations for EM fields far from sources[edit]
Introduction to M-theory In non-technical terms, M-theory presents an idea about the basic substance of the universe. Background[edit] In the early years of the 20th century, the atom – long believed to be the smallest building-block of matter – was proven to consist of even smaller components called protons, neutrons and electrons, which are known as subatomic particles. Beginning in the 1960s, other subatomic particles were discovered. In the 1970s, it was discovered that protons and neutrons (and other hadrons) are themselves made up of smaller particles called quarks. Quantum theory is the set of rules that describes the interactions of these particles. In the 1980s, a new mathematical model of theoretical physics called string theory emerged. These "strings" vibrate in multiple dimensions, and depending on how they vibrate, they might be seen in three-dimensional space as matter, light, or gravity. Status[edit] See also[edit] Superstring theory References[edit] Further reading[edit] External links[edit]
Laser Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers Among their many applications, lasers are used in optical disk drives, laser printers, and barcode scanners; fiber-optic and free-space optical communication; laser surgery and skin treatments; cutting and welding materials; military and law enforcement devices for marking targets and measuring range and speed; and laser lighting displays in entertainment. Fundamentals Lasers are characterized according to their wavelength in a vacuum. Terminology Laser beams in fog, reflected on a car windshield The word laser started as an acronym for "light amplification by stimulated emission of radiation". A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. Design Components of a typical laser: 1. Animation explaining the stimulated emission and the laser principle Laser physics Stimulated emission Gain medium and cavity The light emitted History
Atom Diagram Want to stay on top of all the space news? Follow @universetoday on Twitter A simple carbon atom. The image on the left is a basic atom diagram. This one shows the protons, neutrons, and electrons of a carbon atom. Each is in a group of six. Scientists have used atomic diagrams to explain the workings of the world for centuries. Basic chemistry explains the atom best. Earlier, I mentioned that there had been many atom models developed. The atom diagram is under constant revision as science uncovers more information about sub-atomic particles. Sources:WikipediaChemistry Help Tagged as: atom diagram Polarization (waves) Circular polarization on rubber thread, converted to linear polarization Polarization (also polarisation) is a property of waves that can oscillate with more than one orientation. Electromagnetic waves such as light exhibit polarization, as do some other types of wave, such as gravitational waves. Sound waves in a gas or liquid do not exhibit polarization, since the oscillation is always in the direction the wave travels. The most common optical materials (such as glass) are isotropic and simply preserve the polarization of a wave but do not differentiate between polarization states. Polarization is an important parameter in areas of science dealing with transverse wave propagation, such as optics, seismology, radio, and microwaves. Most sources of light are classified as incoherent and unpolarized (or only "partially polarized") because they consist of a random mixture of waves having different spatial characteristics, frequencies (wavelengths), phases, and polarization states. and . ).
String theory String theory was first studied in the late 1960s[3] as a theory of the strong nuclear force before being abandoned in favor of the theory of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. Five consistent versions of string theory were developed until it was realized in the mid-1990s that they were different limits of a conjectured single 11-dimensional theory now known as M-theory.[4] Many theoretical physicists, including Stephen Hawking, Edward Witten and Juan Maldacena, believe that string theory is a step towards the correct fundamental description of nature: it accommodates a consistent combination of quantum field theory and general relativity, agrees with insights in quantum gravity (such as the holographic principle and black hole thermodynamics) and has passed many non-trivial checks of its internal consistency.
Spectral line Continuous spectrum Absorption lines for air, under indirect illumination, with the direct light source not visible, so that the gas is not directly between source and detector. Here, Fraunhofer lines in sunlight and Rayleigh scattering of this sunlight is the "source." This is the spectrum of a blue sky somewhat close to the horizon, pointing east at around 3 or 4 pm (i.e., Sun in the West) on a clear day. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies. Types of line spectra[edit] Spectral lines are the result of interaction between a quantum system (usually atoms, but sometimes molecules or atomic nuclei) and a single photon. Depending on the type of gas, the photon source and what reaches the detector of the instrument, either an emission line or an absorption line will be produced. Nomenclature[edit] Natural broadening[edit]
Casimir effect Casimir forces on parallel plates A water wave analogue of the Casimir effect. Two parallel plates are submerged into colored water contained in a sonicator. When the sonicator is turned on, waves are excited imitating vacuum fluctuations; as a result, the plates attract to each other. The typical example is of two uncharged metallic plates in a vacuum, placed a few nanometers apart. Dutch physicists Hendrik B. In modern theoretical physics, the Casimir effect plays an important role in the chiral bag model of the nucleon; and in applied physics, it is significant in some aspects of emerging microtechnologies and nanotechnologies.[8] Any medium supporting oscillations has an analogue of the Casimir effect. Overview[edit] Possible causes[edit] Vacuum energy[edit] Main article: Vacuum energy Summing over all possible oscillators at all points in space gives an infinite quantity. Relativistic van der Waals force[edit] Effects[edit] . ). depends on the shape, and so one should write , at point p.