Radio wave
Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter (3⁄64 inch), about the diameter of a grain of rice.Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents.Radio waves were first predicted by the theory of electromagnetism that was proposed in 1867 by Scottish mathematical physicist James Clerk Maxwell.[5] His mathematical theory, now called Maxwell's equations, predicted that a coupled electric and magnetic field could travel through space as an "electromagnetic wave".Radio waves are produced artificially by time-varying electric currents, consisting of electrons flowing back and forth in a specially shaped metal conductor called an antenna.From quantum mechanics, like other electromagnetic radiation such as light, radio waves can alternatively be regarded as streams of uncharged elementary particles called photons.A plane-polarized radio wave has an electric field that oscillates in a plane perpendicular to the direction of motion.In a circularly polarized wave the electric field at any point rotates about the direction of travel, once per cycle.The polarization of radio waves is determined by a quantum mechanical property of the photons called their spin.Plane polarized radio waves consist of photons in a quantum superposition of right and left hand spin states.Radio waves passing through different environments experience reflection, refraction, polarization, diffraction, and absorption.Different frequencies experience different combinations of these phenomena in the Earth's atmosphere, making certain radio bands more useful for specific purposes than others.At the sending end, the information to be sent, in the form of a time-varying electrical signal, is applied to a radio transmitter.The oscillating electric field of the wave causes polar molecules to vibrate back and forth, increasing the temperature; this is how a microwave oven cooks food.A strong enough beam of radio waves can penetrate the eye and heat the lens enough to cause cataracts.Radiofrequency electromagnetic fields have been classified by the International Agency for Research on Cancer (IARC) as having "limited evidence" for its effects on humans and animals.Power density is most accurately used when the point of measurement is far enough away from the RF emitter to be located in what is referred to as the far field zone of the radiation pattern.When speaking of frequencies in the microwave range and higher, power density is usually used to express intensity since exposures that might occur would likely be in the far field zone.
Radio frequencyRadio frequency engineeringRadio Wave 96.5Radio Waveshalf-wave dipoleantennaelectric fieldradio transmitteralternating electric currentpositivenegativespeed of lightelectromagnetic radiationfrequencieswavelengthselectromagnetic spectrumgigahertzmicrowavescharged particlesaccelerationelectric currentslightningastronomical objectsblackbody radiationtransmitterradio receiverradio communicationbroadcastingradio navigationcommunications satelliteswireless computer networksdiffractground wavesionosphereskywavesline of sightinterferenceInternational Telecommunication Unionelectromagnetic wavesradio spectrumelectric fieldsmagnetic fieldsmonopoleHistory of radioelectromagnetismJames Clerk MaxwellMaxwell's equationselectricmagnetic fieldelectromagnetic waveHeinrich Hertzstanding wavesrefractiondiffractionpolarizationGuglielmo MarconiNobel Prize in Physicselectronswavelengthacceleratedradio noiseastronomical radio sourcesblack body radiationquantum mechanicselementary particlesphotonscoherentin phasePlanck's relationjoulesmolecular electron transitionclassicalpermeabilitypermittivityfrequencymegahertzAM bandhorizontally polarizedvertically polarizedcircularly polarizedright circularly polarizedleft circularly polarizedright-hand sensedipole antennaquantum mechanicalquantum superpositionRadio propagationSatellite radioInternet radioTalk radioInternet talk radioMusic radioCall-in (radio)Radio stationMost listened-to programsRadio towerRadio signalpropagationreflectionabsorptionradio bandshorizoncell phonestelevision broadcastingdish antennasmicrowave relayGround stationssatellitescordless phoneswalkie-talkieswireless networksmultipath propagationinterferefadingmedium wavelongwavesurface wavesvery low frequencyextremely low frequencycommunicate with submerged submarinesshortwaveover-the-horizon (OTH) radarradio amateursmicrowavemillimeter waveterahertz band