I've heard and read about the passive sign convention, but don't really understand its meaning and importance in solving electric circuits. Is this because of conventional current which flows opposite electrons or is it something else?
Electronic – What’s passive about the passive sign convention
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Best Answer
The passive sign convention is necessary to determine whether a circuit element is dissipating power, like a resistor, or providing power to the circuit. To calculate an element's power using P=VI you have to measure the voltage across the element. Suppose you use a voltmeter and you connect the red lead to one terminal of the element and the black lead to the other terminal...by doing this you have designated the terminal with the red lead as the posiitive "+" terminal. The passive sign convention says that you must measure the current entering the positive terminal and multiply by the voltage measurement to calculate the element's power. If the result is positive the element is dissipating power, if it is negative the element is supplying power to the circuit.
Of course, the choice of where to put the red lead is arbitrary. But if you reverse the connections and measure the current into the other terminal, then the signs of both the current and voltage will change and their product will still have the same sign. If current is actually flowing out of a terminal then the equivalent current flowing in to the terminal is a negative value.