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VOLTAGE POLARITY AND CURRENT DIRECTION Basic DC Theory VOLTAGE POLARITY AND CURRENT DIRECTION Before  introducing  the  laws  associated  with  complex  DC  circuit  analysis,  the importance  of  voltage  polarity  and  current  direction  must  be  understood.   This chapter  will  introduce  the  polarities  and  current  direction  associated  with  DC circuits. EO 1.10 DESCRIBE  the  difference  between  electron  flow  and conventional current flow. EO 1.11 Given  a  circuit  showing  current  flows,  IDENTIFY  the polarity of the voltage drops in the circuit. Conventional and Electron Flow The  direction  of  electron  flow  is  from  a  point  of  negative  potential  to  a  point  of  positive potential.   The  direction  of  positive  charges,  or  holes,  is  in  the  opposite  direction  of  electron flow.   This flow of positive charges is known as conventional flow.   All of the electrical effects of electron flow from negative to positive, or from a high potential to a lower potential, are the same  as  those  that  would  be  created  by  flow  of  positive  charges  in  the  opposite  direction; therefore,  it  is  important  to  realize  that  both  conventions  are  in  use,  and  they  are  essentially equivalent.   In this manual, the electron flow convention is used. Polarities All voltages and currents have polarity as well as magnitude.   In a series circuit, there is only one current, and its polarity is from the negative battery terminal through the rest of the circuit to the positive battery terminal.  Voltage drops across loads also have polarities.  The easiest way to find these polarities is to use the direction of the electron current as a basis.   Then, where the electron current enters the load, the voltage is negative (Figure 31).   This holds true regardless of the number or type of loads in the circuit.   The drop across the load is opposite to that of the source.   The voltage drops oppose the source voltage and reduce it for the other loads.   This is because each load uses energy, leaving less energy for other loads. ES-02 Page 40 Rev. 0


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