Voltage Difference in Electric Circuit

Voltage difference is analogous to pressure difference and is defined as the differential amount of charge and energy

(3.5)

Where dw is the incremental energy required to move an incremental charge dq through a voltage difference of V.

• The voltage represents the greatest difference of potential between any two points in a circuit.

• The voltage cannot flow; however, it pushes current through the circuit.

• Voltage must be present before current can flow, just as pressure must be present before water can flow.

• Also, a voltage can exist between a pair of electrical terminals whether a current is flowing or not.

• An automobile battery, for example, has a voltage of 12 V across its terminals even if nothing is connected to the terminals.
  
  

Figure 3.1 A two-terminal circuit.

The letter E is used to indicate a voltage rise and the letter V is used to indicate a voltage drop. A plus-minus pair of algebraic signs indicates the sense of the voltage. The placement of the + sign at terminal A indicates that terminal A is V volts positive with respect to terminal B as (see Figure 3.1). If V happens to have a numerical value of –2 V, then we may say either that A is –2 V positive with respect to B or that B is 2 V positive with respect to A. The sign also indicates the polarity of a terminal, i.e. its particular state (positive or negative).