What is the effect of increasing electrode size on current density at the tissue interface?

• A. Increases current density
• B. Reduces current density and spreads the dose
• C. Has no effect on current density
• D. Changes only the frequency of the current

Answer: (B)

Current density at the tissue interface is the amount of current per unit area (J = I/A). If you keep the same total current but enlarge the electrode area, the current per unit area drops. That means the electrical dose is distributed over a larger area, producing a more diffuse stimulation with a lower peak intensity at any single spot. The frequency of the current is determined by the device, not the electrode size, so changing electrode size doesn’t alter frequency. Therefore, increasing electrode size reduces current density and spreads the dose.