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(wavelength of an electromagnetic wave in vacuum = the speed of light divided by the wave's frequency).
(wavelength of an electromagnetic wave in vacuum = the speed of light divided by the wave's frequency).
The speed of light is about one foot per nanosecond. The late computer pioneer Admiral Grace Hopper was fond of keeping foot-long lengths of wire in her purse; she used them as props for her talks, referring to them as "nanoseconds," and using them to explain how the speed of light set limitations on computing systems (Although the rate of energy propagation in copper wire is significantly lower than the speed of light).<ref>Chiarella, Donald Joseph Gray (2002), ''Life in God's Management Corps,'' [http://books.google.com/books?vid=ISBN0595256430&id=VhM9jDwbywUC&pg=PA14&lpg=PA14&ots=ZXHirs9jQI&dq=grace+hopper+nanosecond&ie=ISO-8859-1&sig=XmbYtV2laxCMIKMLzR1eXHP1Eok p. 14]</ref>
The speed of light is about one foot per nanosecond. The late computer pioneer Admiral Grace Hopper was fond of keeping foot-long lengths of wire in her purse; she used them as props for her talks, referring to them as "nanoseconds," and using them to explain how the speed of light set limitations on [[computing]] systems (Although the rate of energy propagation in copper wire is significantly lower than the speed of light).<ref>Chiarella, Donald Joseph Gray (2002), ''Life in God's Management Corps,'' [http://books.google.com/books?vid=ISBN0595256430&id=VhM9jDwbywUC&pg=PA14&lpg=PA14&ots=ZXHirs9jQI&dq=grace+hopper+nanosecond&ie=ISO-8859-1&sig=XmbYtV2laxCMIKMLzR1eXHP1Eok p. 14]</ref>
The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. When a charged particle exceeds the speed of light in the medium in which it is travelling, it emits [[Cherenkov Radiation]].
The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. When a charged particle exceeds the speed of light in the medium in which it is travelling, it emits [[Cherenkov Radiation]].