Why does voltage sign matter for electrical devices and components
Why does the sign matter?


It matters because many electronic components only work with current in one direction.







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Figure 1. Polarity sensitive components.


D1, a diode, has a symbol which shows the direction of current flow (in the direction of the arrow). If the polarity is reversed current cannot flow.
Q1 and Q2 are transistors. Again, the arrows in the symbols show the direction of current flow, top to bottom as drawn. A circuit's design will take this into consideration and it will not function if polarity is reversed.
Integrated circuits such as op-amps and microcontrollers contain several or thousands of transistors of one type or another and the whole circuit is polarity sensitive.


Circuits using passive components only, resistors, capacitors and inductors, are not polarity sensitive.







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Figure 2. A bridge rectifier accepts input of either polarity or alternating and converts it to DC of the required polarity.

Circuits can be designed in certain applications which are not polarity sensitive and can even work on AC power. Typically these use a rectifier to "rectify" the input voltage to the correct polarity.