The passive sign convention is a widely used convention in electrical engineering to define the polarity and direction of voltage, current, and power in circuit elements such as resistors, capacitors, and inductors. This convention helps maintain consistency and clarity when analyzing and designing electrical circuits.
Resistors:
For resistors, the passive sign convention states that the current through the resistor flows from the higher potential (voltage) terminal to the lower potential terminal. In other words, the positive terminal of the resistor is where the current enters, and the negative terminal is where it exits. The voltage drop across a resistor is considered positive when the current enters the positive terminal and negative when it enters the negative terminal.
Capacitors:
For capacitors, the passive sign convention is based on the change in voltage across the capacitor and the direction of the current flow. When a capacitor is charging, the current flows into the positive terminal of the capacitor. The voltage across the capacitor is considered positive when the voltage at the positive terminal is higher than at the negative terminal. During discharge, the current flows out of the positive terminal, and the voltage across the capacitor is considered negative when the voltage at the positive terminal is lower than at the negative terminal.
Inductors:
For inductors, the passive sign convention is also based on the direction of current flow and the resulting voltage polarity. When the current through an inductor increases, the voltage across it is considered positive at the terminal where the current enters and negative at the terminal where it exits. Conversely, when the current decreases, the voltage across the inductor is considered negative at the terminal where the current enters and positive at the terminal where it exits.
In summary, the passive sign convention is a consistent way to define the positive and negative polarity of voltage, current, and power for resistors, capacitors, and inductors, making circuit analysis and design more straightforward and standardized.