Why is the indifferent electrode larger than the needle in galvanic electrolysis?

In galvanic electrolysis, the indifferent electrode is designed to be larger than the needle electrode to minimize the localized effects of electrical current and subsequent chemical reactions on the skin. A larger indifferent electrode spreads out the electrical current over a greater surface area, which helps to ensure that the current density is lower. This reduction in current density decreases the risk of skin irritation, electrochemical burns, or adverse reactions at the site of application.

When the current is distributed more evenly, it reduces the likelihood of excessive local heating or chemical accumulation from ionic reactions. This is particularly important to ensure patient safety and comfort during the procedure. Therefore, while the size of the electrodes may affect other factors like handling or voltage, the primary purpose of the larger indifferent electrode is to minimize negative effects on the skin.