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Key Terms

displacement current
extra term in Maxwell’s equations that is analogous to a real current but accounts for a changing electric field producing a magnetic field, even when the real current is present
gamma ray (γγ ray)
extremely high frequency electromagnetic radiation emitted by the nucleus of an atom, either from natural nuclear decay or induced nuclear processes in nuclear reactors and weapons; the lower end of the γγ -ray frequency range overlaps the upper end of the X-ray range, but γγ rays can have the highest frequency of any electromagnetic radiation
infrared radiation
region of the electromagnetic spectrum with a frequency range that extends from just below the red region of the visible light spectrum up to the microwave region, or from 0.74μm to300μm0.74μm to300μm
Maxwell’s equations
set of four equations that comprise a complete, overarching theory of electromagnetism
electromagnetic waves with wavelengths in the range from 1 mm to 1 m; they can be produced by currents in macroscopic circuits and devices
Poynting vector
vector equal to the cross product of the electric-and magnetic fields, that describes the flow of electromagnetic energy through a surface
common application of microwaves; radar can determine the distance to objects as diverse as clouds and aircraft, as well as determine the speed of a car or the intensity of a rainstorm
radiation pressure
force divided by area applied by an electromagnetic wave on a surface
radio waves
electromagnetic waves with wavelengths in the range from 1 mm to 100 km; they are produced by currents in wires and circuits and by astronomical phenomena
thermal agitation
thermal motion of atoms and molecules in any object at a temperature above absolute zero, which causes them to emit and absorb radiation
ultraviolet radiation
electromagnetic radiation in the range extending upward in frequency from violet light and overlapping with the lowest X-ray frequencies, with wavelengths from 400 nm down to about 10 nm
visible light
narrow segment of the electromagnetic spectrum to which the normal human eye responds, from about 400 to 750 nm
invisible, penetrating form of very high frequency electromagnetic radiation, overlapping both the ultraviolet range and the γγ-ray range
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