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# Mathematical Meaning of 'Normal'

March 8th Fact-of-the-Day

Familiarity 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.