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.
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