CT: Besides natural sources, the electromagnetic spectrum also includes fields generated by human-made sources: X-rays are employed to diagnose a broken limb after a sport accident. The electricity that comes out of every power socket has associated low frequency electromagnetic fields. And various kinds of higher frequency radiowaves are used to transmit information – whether via TV antennas, radio stations or mobile phone base stations.
S: WHO – http://www.who.int/peh-emf/about/WhatisEMF/en/ (last access: 17th December 2014).
N: 1. electromagnetic (adj): also electro-magnetic, 1821; see electro- (before vowels electr-, word-forming element meaning “electrical, electricity,” Latinized form of Greek elektro-, comb. form of elektron “amber”; as a stand-alone, formerly often short for electrotype, electroplate) + magnetic (1610s, literal; 1630s, figurative, from Modern Latin magneticus, from Latin magnes).
field (n): Old English feld “plain, pasture, open land, cultivated land” (as opposed to woodland), also “a parcel of land marked off and used for pasture or tillage,” probably related to Old English folde “earth, land,” from Proto-Germanic felthuz “flat land”. This is from PIE pel(e)-tu-, from root pele- “flat, to spread”. Physics sense is from 1845.
2. Electromagnetic field, a property of space caused by the motion of an electric charge. A stationary charge will only produce an electric field in the surrounding space.
3. Electromagnetic fields are present everywhere in our environment, but are invisible to the human eye.
4. One of the main characteristics which defines an electromagnetic field (EMF) is its frequency or its corresponding wavelength
S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=field&searchmode=none (last access: 17th December 2014). 2. EncBrit – http://global.britannica.com/EBchecked/topic/183201/electromagnetic-field (last access: 17th December 2014). 3 & 4. WHO – http://www.who.int/peh-emf/about/WhatisEMF/en/ (last access: 17th December 2014).