20. When the height of burst is varied for some given explosion, the strength ofthe EI"{P signal received at some given distance from ground zero vi1I varyconsiderably. surface or low air bu"sts of a weapon of moderate size vrr-r- generatezuF that nay have hamfur effects on electrical and electronic equipnent ou! r,o adistance of about 3-IO krn. (2 to 6 mi].es) from ground zero, depending on theexpl0sion yield and the equiprlent sensitivity. The strength oi th. fu,fp ut tnugrourid- will then decrease vith increasing height of burst up to an artitude of ca.10 to 15 kr. (35,Ooo to 5o,ooo ft.). WtrJn nuists oceur at still higher attitud.es,a sirong s4P vill again be experienced. an the ground. This is due to the combinedeffects of atmospheric density variation *ith ;ftitude and the geomagnetic field.Thls flvIP covers a wide area, since it extends outvards in alr- directions as far asthe line-of-sight fron the burst point. A nuclear explosion at an aftitude ofBo kn' vould affect a circurar area vith a radius of about 1,000 km. and an altitudeof 160 kn. (roo mires) would produce effects over a circ.'1ar area wlth a radius ofabout 1,500 kn. (900 miles), Thus a high altitude burst might cause EMp d.smage atground vhere all other effects (exceFt possibly flash blindness at night) vould benF,'lidihla 2f' The EMP energy is coffected in antennae - or obJects serving as 'nintentional antennae - just as the energy of ordinary radio vaves. Depending on the length andorientation of the antenns. - as well as whether it is in tfre airl on or slight.Lyunder the ground - it will collect more or fess EMp energy. ruis enerly might thenbe transported - sometines over large distances - to electrical or e.rectronicsystems ccnnected to its ends. The farger the antenna - or 'nintended antenna,such as a telephone or electrical vire _ the mo"e Fjl.4p energy it will co1lect.
**Analysis**
The text appears to be discussing the effects of a nuclear explosion on the environment, specifically the electromagnetic pulse (EMP) generated by the explosion and its impact on electrical and electronic equipment. The text provides technical details about the range and effects of the EMP, as well as its potential to cause damage to equipment and systems.

**Category**
Science and technology, Transport and communication