General considerations Occurrence and importance Close to 0. All human life is immersed in it, and modern communications technology and medical services are particularly dependent on one or another of its forms.
Theory[ edit ] Shows the relative wavelengths of the electromagnetic waves of three different colours of light blue, green, and red with a distance scale in micrometers along the x-axis. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of lightMaxwell concluded that light itself is an EM wave.
According to Maxwell's equationsa spatially varying electric field is always associated with a magnetic field that changes over time. In an electromagnetic wave, the changes in the electric field are always accompanied by a wave in the magnetic field in one direction, and vice versa.
This relationship between the two occurs without either type field causing the other; rather, they occur together in the same way that time and space changes occur together and are interlinked in special relativity. In fact, magnetic fields can be viewed as electric field in other frame of reference s ' and electric fields which can be viewed also as magnetic fields in other frame of reference sbut they have equal significance as physics is same in all frame of reference s.
Together, these fields form a propagating electromagnetic wave, which moves out into space and need never again affect the source. The distant EM field formed in this way by the acceleration of a charge carries energy with it that "radiates" away through space, hence the term.
Near and far fields[ edit ] Main articles: Electromagnetic radiation thus includes the far field part of the electromagnetic field around a transmitter.
A part of the "near-field" close to the transmitter, forms part of the changing electromagnetic fieldbut does not count as electromagnetic radiation. Maxwell's equations established that some charges and currents "sources" produce a local type of electromagnetic field near them that does not have the behaviour of EMR.
Currents directly produce a magnetic field, but it is of a magnetic dipole type that dies out with distance from the current.
In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential such as in an antenna produce an electric dipole type electrical field, but this also declines with distance.
These fields make up the near-field near the EMR source. Neither of these behaviours are responsible for EM radiation. Instead, they cause electromagnetic field behaviour that only efficiently transfers power to a receiver very close to the source, such as the magnetic induction inside a transformeror the feedback behaviour that happens close to the coil of a metal detector.
This distant part of the electromagnetic field is "electromagnetic radiation" also called the far-field. The far-fields propagate radiate without allowing the transmitter to affect them.
This causes them to be independent in the sense that their existence and their energy, after they have left the transmitter, is completely independent of both transmitter and receiver. Due to conservation of energythe amount of power passing through any spherical surface drawn around the source is the same.
Because such a surface has an area proportional to the square of its distance from the source, the power density of EM radiation always decreases with the inverse square of distance from the source; this is called the inverse-square law.
This is in contrast to dipole parts of the EM field close to the source the near-fieldwhich varies in power according to an inverse cube power law, and thus does not transport a conserved amount of energy over distances, but instead fades with distance, with its energy as noted rapidly returning to the transmitter or absorbed by a nearby receiver such as a transformer secondary coil.
Whereas the magnetic part of the near-field is due to currents in the source, the magnetic field in EMR is due only to the local change in the electric field. In a similar way, while the electric field in the near-field is due directly to the charges and charge-separation in the source, the electric field in EMR is due to a change in the local magnetic field.
Both processes for producing electric and magnetic EMR fields have a different dependence on distance than do near-field dipole electric and magnetic fields. Now independent of the source charges, the EM field, as it moves farther away, is dependent only upon the accelerations of the charges that produced it.
It no longer has a strong connection to the direct fields of the charges, or to the velocity of the charges currents.
By contrast, the term associated with the changing static electric field of the particle and the magnetic term that results from the particle's uniform velocity, are both associated with the electromagnetic near-field, and do not comprise EM radiation.
This 3D animation shows a plane linearly polarized wave propagating from left to right. Note that the electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.
Electrodynamics is the physics of electromagnetic radiation, and electromagnetism is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties of superposition.
Thus, a field due to any particular particle or time-varying electric or magnetic field contributes to the fields present in the same space due to other causes. Further, as they are vector fields, all magnetic and electric field vectors add together according to vector addition. However, in nonlinear media, such as some crystalsinteractions can occur between light and static electric and magnetic fields — these interactions include the Faraday effect and the Kerr effect.
The ratio of the refractive indices of the media determines the degree of refraction, and is summarized by Snell's law. Light of composite wavelengths natural sunlight disperses into a visible spectrum passing through a prism, because of the wavelength-dependent refractive index of the prism material dispersion ; that is, each component wave within the composite light is bent a different amount.In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.
This includes: electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ); particle radiation, such as alpha radiation (α), beta radiation (β), and neutron radiation (particles of. The Electromagnetic Spectrum Overview continued Curriculum Overview: Introduction to the Electromagnetic Spectrum In the matter of physics, the first lessons should contain nothing but what is.
A simple introduction to the electromagnetic spectrum ranging from X-rays to radio waves, but with the emphasis on the UV and visible regions.
ELECTROMAGNETIC RADIATION This page is a basic introduction to the electromagnetic spectrum sufficient for chemistry students interested in UV-visible absorption spectroscopy.
The electromagnetic spectrum represents all of the possible frequencies of electromagnetic energy. It ranges from extremely long wavelengths (extremely low frequency exposures such as those from power lines) to extremely short wavelengths (x-rays and gamma rays) and includes both non-ionizing and ionizing radiation.
Electromagnetic radiation composed of photons that carry minimum-ionization energy, or more, (which includes the entire spectrum with shorter wavelengths), is therefore termed ionizing radiation. (Many other kinds of ionizing radiation are made of non-EM particles). Electromagnetic radiation is composed of oscillating electric and magnetic fields that have the ability to transfer energy through space.
The energy propagates as a wave, such that the crests and troughs of the wave move. General considerations Occurrence and importance.