# Mathematical Meaning of 'Normal'

March 8th Fact-of-the-DayFamiliarity with
common meanings of the word 'normal,' such as 'being approximately
average' or 'conforming to convention,' can make mathematical papers on
subjects such as the electric, magnetic and electromagnetic fields surrounding
antennas confusing to non-mathematicians, because 'normal' has a special
meaning in mathematics. In mathematics the word 'normal' means 'perpendicular.'
Therefore to a mathematician, a vertical antenna is an antenna that is
normal to earth. A feedline that comes away from a radiator at a right
angle is normal to the radiator. The direction of electromagnetic propagation
from an antenna is normal to a curve drawn around the antenna if it is
perpendicular to a tangent line to the curve at the point where it intersects
the curve. Students of linear algebra will know that two vectors are normal
to each other if their dot product is zero. *©2005 Martek International
All rights reserved.*

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