
 What is impedance?  a definition from Whatis.com 
   Impedance, denoted Z, is an expression of the opposition that an electronic component, circuit, or system offers to alternating and/or direct electric current.Impedance is a vector (twodimensional)quantity consisting of two independent scalar (onedimensional) phenomena: resistance and reactance. 
  Resistance, denoted R, is a measure of the extent to which a substance opposes the movement of electrons among its atoms.The more easily the atoms give up and/or accept electrons, the lower the resistance, which is expressed in positive real number ohms.Resistance is observed with alternating current (AC) and also with direct current (DC). 
  Suppose a resistance of 100.00 ohms is connected in a series circuit with an inductance of 10.000 ?H.At 4.0000 MHz, the complex impedance is: 
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