Figure 30-28 Resistance and capacitance in a direct-current circuit. A, Under direct current, the resistance impedes flow, with a voltage drop developing across the resistance. The capacitor allows current to flow until the charge builds on the capacitor (B). Under direct current, the voltage is constant over time, and the current flow decreases as the charge on the capacitor increases. This type of circuit is used to charge a defibrillator.