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. In a classical description, the lack of an external field also means that there is no field between the plates, and no force would be measured between them.[1] When this field is instead studied using the QED vacuum of quantum electrodynamics, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force[2]—either an attraction or a repulsion depending on the specific arrangement of the two plates.
Dutch physicists Hendrik B. G. Any medium supporting oscillations has an analogue of the Casimir effect. Overview[edit] Possible causes[edit] Vacuum energy[edit] . ). 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] 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. However there are important classes of materials classified as birefringent or optically active in which this is not the case and a wave's polarization will generally be modified or will affect propagation through it.
A polarizer is an optical filter that transmits only one polarization. and where λ/n is the wavelength in the medium (whose refractive index is n) and T = 1/f is the period of the wave. . Where . 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. Most "single wavelength" lasers actually produce radiation in several modes having slightly differing frequencies (wavelengths), often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously.
There are some lasers that are not single spatial mode and consequently have light beams that diverge more than is required by the diffraction limit. Design. 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 a vacuum, it propagates at a characteristic speed, the speed of light, normally in straight lines. EMR is emitted and absorbed by charged particles. In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. Physics[edit] Theory[edit] Maxwell’s equations for EM fields far from sources[edit] 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. Molecule. Atom. The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other by chemical bonds based on the same force, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as an ion.
An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.[1] Etymology History of atomic theory Atomism First evidence-based theory The structure of atoms The physicist J. Structure.