electromagnetic radiation

Examples of electromagnetic radiation in the following topics:

• Planck's Quantum Hypothesis and Black Body Radiation

  • A black body emits radiation called black body radiation.
  • A black body in thermal equilibrium (i.e. at a constant temperature) emits electromagnetic radiation called black body radiation.
  • Max Planck, in 1901, accurately described the radiation by assuming that electromagnetic radiation was emitted in discrete packets (or quanta).
  • Contrary to the common belief that electromagnetic radiation can take continuous values of energy, Planck introduced a radical concept that electromagnetic radiation was emitted in discrete packets (or quanta) of energy.
  • Identify assumption made by Max Planck to describe the electromagnetic radiation emitted by a black body

• Photon Energies of the EM Spectrum

  • The electromagnetic (EM) spectrum is the range of all possible frequencies of electromagnetic radiation.
  • The electromagnetic (EM) spectrum is the range of all possible frequencies of electromagnetic radiation .
  • In 1886, the physicist Hertz built an apparatus to generate and detect what are now called radio waves, in an attempt to prove Maxwell's equations and detect such low-frequency electromagnetic radiation.
  • However, in 1910, British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles.
  • Generally, electromagnetic radiation is classified by wavelength into radio waves, microwaves, terahertz (or sub-millimeter) radiation, infrared, the visible region humans perceive as light, ultraviolet, X-rays, and gamma rays.

• Energy and Momentum

  • Electromagnetic radiation can essentially be described as photon streams.
  • Planck theorized that "black bodies" (thermal radiators) and other forms of electromagnetic radiation existed not as spectra, but in discrete, "quantized" form.
  • In other words, there were only certain energies an electromagnetic wave could have.
  • Momentum is classically defined as the product of mass and velocity and thus would intuitively seem irrelevant to a discussion of electromagnetic radiation, which is both massless and composed of waves.
  • Relate energy of an electromagnetic wave with the frequency and wavelength

• Fluorescence and Phosphorescence

  • Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
  • In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation.
  • However, when the absorbed electromagnetic radiation is intense, it is possible for one electron to absorb two photons; this two-photon absorption can lead to emission of radiation having a shorter wavelength than the absorbed radiation.
  • The emitted radiation may also be of the same wavelength as the absorbed radiation, termed "resonance fluorescence".
  • Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs.

• Radiation

  • We use different names for electromagnetic waves of different wavelengths: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays .
  • The energy of electromagnetic radiation depends on its wavelength (color) and varies over a wide range; a smaller wavelength (or higher frequency) corresponds to a higher energy.
  • All objects absorb and emit electromagnetic radiation.
  • Gray objects have a uniform ability to absorb all parts of the electromagnetic spectrum.
  • (a) A graph of the spectra of electromagnetic waves emitted from an ideal radiator at three different temperatures.

• The Production of Electromagnetic Waves

  • Electromagnetic waves are the combination of electric and magnetic field waves produced by moving charges.
  • Electromagnetic radiation, is a form of energy emitted by moving charged particles.
  • The creation of all electromagnetic waves begins with a charged particle.
  • These and many more such devices use electromagnetic waves to transmit data and signals.
  • Electromagnetic waves are a self-propagating transverse wave of oscillating electric and magnetic fields.

• Infrared Waves

  • Infrared (IR) light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 0.74 micrometers (µm) to 1 mm.
  • Infrared radiation is popularly known as "heat radiation," but light and electromagnetic waves of any frequency will heat surfaces that absorb them.
  • As stated above, while infrared radiation is commonly referred to as heat radiation, only objects emitting with a certain range of temperatures and emissivities will produce most of their electromagnetic emission in the infrared part of the spectrum.
  • This is a plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation.
  • The electromagnetic spectrum, showing the major categories of electromagnetic waves.

• Microwaves

  • EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered as far infrared light, also referred to as terahertz radiation.
  • Microwaves can also be produced by atoms and molecules—e.g., they are a component of electromagnetic radiation generated by thermal agitation.
  • The Cosmic Microwave Background Radiation (CMBR) is microwave radiation that permeates all of space, and its discovery supports the Big Bang theory of the origin of the universe.
  • Cosmic background radiation of the Big Bang mapped with increasing resolution.
  • The electromagnetic spectrum, showing the major categories of electromagnetic waves.

• X-Rays

  • In many languages, X-radiation is called Röntgen radiation, after Wilhelm Röntgen, who is usually credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation.
  • The electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength than the radiation emitted by radioactive nuclei.
  • Like all electromagnetic radiation, the properties of X-rays (or gamma rays) depend only on their wavelength and polarization.
  • X-rays are part of the electromagnetic spectrum, with wavelengths shorter than those of visible light.
  • The electromagnetic spectrum, showing the major categories of electromagnetic waves.

• A Physical Aside: Multipole Radiation

  • It is possible to calculate the radiation field to higher order in $L/(c\tau)$.This is necessary if the dipole moment vanishes, for example.
  • where $k\equiv\omega/c$$n=0$ gives the dipole radiation, $n=1$ gives the quadrupole radiation and so on.
  • The propagation of electromagnetic waves from a source traveling slower and faster than the speed of light in the medium.