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Light - Light as electromagnetic radiation: In spite of theoretical and experimental advances in the first half of the 19th century that established the wave. By definition, visible light is the part of the EM spectrum the human eye is the most sensitive to. Visible light (and. Light is a form of electromagnetism. The electromagnetic spectrum is a range of all types electromagnetic radiation. Within that spectrum is the light in your.
To this end we employ the position-momentum commutator bracket, and invoked a photon wavefunction. This wavefunction is constructed from the linear complex combination of the electric and magnetic fields. The outcome of the bracket yields three equations defining the photon electric and magnetic fields in terms of its angular momentum. These equations turn out to be very similar to those fields created by a moving charge.
Thus, the electric and magnetic fields of the photon doesn't' require a charge for the photon. It is intriguing that the photon has no charge and mass but has electric and magnetic fields as well as energy. These fields should also satisfy Maxwell's equations. Doing so, yields additional electric and magnetic charge and current densities for the photon.
The emergent Maxwell's equations are now appropriate to describe the photon as a quantum particle. These additional terms in Maxwell's equations are the source in describing the photon quantum electrodynamics behavior. Some emergent phenomena associated with topological insulator, Faraday's rotation effect, Hall effect and Kerr's effect could be examples of this contribution terms to Maxwell's equations. The instrument was capable of detecting a difference in light speeds along the two paths of the interferometer as small as 5, metres per second less than 2 parts inof the speed of light.
No difference was found. If Earth indeed moved through the ether, that motion seemed to have no effect on the measured speed of light. The half-transparent mirror has the same effect on the returning beams, splitting each of them into two beams.
- Light: Electromagnetic waves, the electromagnetic spectrum and photons
Thus, two diminished light beams reach the screen, where interference patterns can be observed by varying the position of the movable mirror. What is now known as the most famous experimental null result in physics was reconciled in when Albert Einsteinin his formulation of special relativitypostulated that the speed of light is the same in all reference frames ; i. The hypothetical ether, with its preferred reference framewas eventually abandoned as an unnecessary construct.
Its significance is far broader than its role in describing a property of electromagnetic waves. It serves as the single limiting velocity in the universebeing an upper bound to the propagation speed of signals and to the speeds of all material particles.
Measurements of the speed of light were successively refined in the 20th century, eventually reaching a precision limited by the definitions of the units of length and time—the metre and the second.
In the 17th General Conference on Weights and Measures fixed the speed of light as a defined constant at exactly , metres per second.
In a longitudinal wave the oscillating disturbance is parallel to the direction of propagation. A familiar example is a sound wave in air—the oscillating motions of the air molecules are induced in the direction of the advancing wave. Transverse waves consist of disturbances that are at right angles to the direction of propagation; for example, as a wave travels horizontally through a body of water, its surface bobs up and down.
A number of puzzling optical effects, first observed in the midth century, were resolved when light was understood as a wave phenomenon and the directions of its oscillations were uncovered. The first so-called polarization effect was discovered by the Danish physician Erasmus Bartholin in Bartholin observed double refractionor birefringence, in calcite a common crystalline form of calcium carbonate.
When light passes through calcite, the crystal splits the light, producing two images offset from each other. Huygens, a contemporary of Newton, could account for double refraction with his elementary wave theory, but he did not recognize the true implications of the effect. Double refraction remained a mystery until Thomas Youngand independently the French physicist Augustin-Jean Fresnelsuggested that light waves are transverse.
This simple notion provided a natural and uncomplicated framework for the analysis of polarization effects. The polarization of the entering light wave can be described as a combination of two perpendicular polarizations, each with its own wave speed. Because of their different wave speeds, the two polarization components have different indices of refraction, and they therefore refract differently through the material, producing two images.
Fresnel quickly developed a comprehensive model of transverse light waves that accounted for double refraction and a host of other optical effects. Double refraction showing two rays emerging when a single light ray strikes a calcite crystal at a right angle to one face. The fields are also perpendicular to one another, with the electric field direction, magnetic field direction, and propagation direction forming a right-handed coordinate system. The equations show that the electric and magnetic fields are in phase with each other; at any given point in space, they reach their maximum values, E0 and B0, at the same time.
In describing the orientation of the electric and magnetic fields of a light wave, it is common practice to specify only the direction of the electric field; the magnetic field direction then follows from the requirement that the fields are perpendicular to one another, as well as the direction of wave propagation.
In reception of radio waves, the oscillating electric and magnetic fields of a radio wave couple to the electrons in an antenna, pushing them back and forth, creating oscillating currents which are applied to a radio receiver.
Earth's atmosphere is mainly transparent to radio waves, except for layers of charged particles in the ionosphere which can reflect certain frequencies. Radio waves are extremely widely used to transmit information across distances in radio communication systems such as radio broadcastingtelevisiontwo way radiosmobile phonescommunication satellitesand wireless networking.
In a radio communication system, a radio frequency current is modulated with an information-bearing signal in a transmitter by varying either the amplitude, frequency or phase, and applied to an antenna. The radio waves carry the information across space to a receiver, where they are received by an antenna and the information extracted by demodulation in the receiver.
Radio waves are also used for navigation in systems like Global Positioning System GPS and navigational beaconsand locating distant objects in radiolocation and radar.
Light - Light as electromagnetic radiation | yogada.info
They are also used for remote controland for industrial heating. The use of the radio spectrum is strictly regulated by governments, coordinated by a body called the International Telecommunications Union ITU which allocates frequencies to different users for different uses. Microwaves Plot of Earth's atmospheric transmittance or opacity to various wavelengths of electromagnetic radiation. Microwaves are radio waves of short wavelengthfrom about 10 centimeters to one millimeter, in the SHF and EHF frequency bands.
Although they are emitted and absorbed by short antennas, they are also absorbed by polar moleculescoupling to vibrational and rotational modes, resulting in bulk heating. Unlike higher frequency waves such as infrared and light which are absorbed mainly at surfaces, microwaves can penetrate into materials and deposit their energy below the surface.
This effect is used to heat food in microwave ovensand for industrial heating and medical diathermy. Microwaves are the main wavelengths used in radarand are used for satellite communicationand wireless networking technologies such as Wi-Fialthough this is at intensity levels unable to cause thermal heating. The copper cables transmission lines which are used to carry lower frequency radio waves to antennas have excessive power losses at microwave frequencies, and metal pipes called waveguides are used to carry them.
Although at the low end of the band the atmosphere is mainly transparent, at the upper end of the band absorption of microwaves by atmospheric gasses limits practical propagation distances to a few kilometers. Terahertz radiation Main article: Terahertz radiation Terahertz radiation is a region of the spectrum between far infrared and microwaves.
Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band sub-millimeter waves or so-called terahertz wavesbut applications such as imaging and communications are now appearing.
Scientists are also looking to apply terahertz technology in the armed forces, where high-frequency waves might be directed at enemy troops to incapacitate their electronic equipment. Infrared radiation Main article: It can be divided into three parts: The lower part of this range may also be called microwaves or terahertz waves.
This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere in effect opaque.