Which statement best describes balance of charge?

• A. The charges are the same size and will cancel if balanced
• B. Balanced charge has no effect on tissue response
• C. If charges are the same size, they will cancel each other out
• D. Balance of charge is irrelevant to current type

Answer: (C)

Charge balance means the total amount of electrical charge delivered to tissue in one part of the waveform is exactly offset by the opposite charge in the other part, so the net charge over a cycle is zero. This happens when the positive and negative phases carry the same amount of charge—that is, they have equal area under the current-time curve, just with opposite polarity.

Why this is best: if the two phases deliver equal charge, there’s no net buildup of charge at the electrode–tissue interface. That prevents unwanted electrochemical reactions, electrode polarization, and potential tissue irritation or damage, making stimulation safer over time. The idea that equal, opposite charges cancel each other out captures the essential safety and tissue-response rationale behind using charge-balanced waveforms.

In contrast, statements suggesting no effect on tissue response, or asserting charge balance is irrelevant to the type of current, miss the safety and physiological implications. If charge isn’t balanced, a net DC component can cause harmful changes at the tissue boundary and with the electrode.