10/4/2005 The Electric Force.doc 1/2 Jim Stiles The Univ. of Kansas Dept. of EECS The Electric Force Say a charge Q is located at some point in space, a point denoted by position vector r. Likewise, there exists everywhere in space an electric field (we neither know nor care how this electric field was created). The value (both magnitude and direction) of the electric field vector at point r is ()rE : Q: Our “field theory” of electromagnetics says that the electric field will apply a force on the charge. Precisely what is this force (i.e., its magnitude and direction)? A: Fortunately, the answer is rather simple! The force Fe on charge Q is the product of the charge ( a scalar) and the value of the electric field (a vector) at the point where the charge is located: []() NerQ=EF r Q ()rE10/4/2005 The Electric Force.doc 2/2 Jim Stiles The Univ. of Kansas Dept. of EECS Note therefore, that the force vector will be parallel (or anti-parallel) to the electric field! Note the magnitude of the electric force will increase proportionally with an increase in charge and/or and increase in the electric field magnitude. Q > 0 (charge is positive) so Fepoints in the same direction asthe electric field. Q < 0 (charge is negative) so Fepoints in the opposite direction asthe electric field. eF+
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