 Welcome to discharging time constants of an RC circuit. A capacitor consists of two plates on which electrostatic charges develop. When it discharges, the voltage across its plates decreased to zero. The diagram below and its graph show the effect of a series RC circuit from the moment a discharge path is provided until five time constants later when the capacitor is fully discharged. During the five time constants, the maximum current throughout the RC circuit will be 10 mA and the minimum current will be 0 mA. The speed at which the capacitor discharges is determined by the value of the capacitor and the value of the resistor. With the switch open, there is no current flow. The voltage charge at the capacitor is 10 volts and the voltage across the resistor is 0 volts as shown at the right. Time constant zero. The instant the switch is closed, it is referred to as time constant zero. The following circuit conditions occur. The capacitor is charged to 10 volts and acts as a power source for the circuit. The capacitor begins to discharge at the fastest possible rate. With the only opposition to current flow from the resistor, current flow is at the maximum value of 10 mA. And the voltage across the resistor is 10 volts. Time constant one. During the first time constant, several circuit values change by 63%. The following conditions occur. The voltage across the capacitor decreases from 10 to 3.7 volts. The remaining 3.7 volts from the capacitor drop across the resistor. The current decreases from 10 mA to 3.7 mA. Time constants 2, 3, and 4. During each of the time constant intervals between 1 to 2, 2 to 3, and 3 to 4, the capacitor voltage, resistor voltage, and circuit current values change by 63%. Here is time constant 2. This is time constant 3. And time constant 4. After 5 time constants, all of the circuit values have changed 100%. The following circuit conditions occur. The capacitor is fully discharged and acts like an open. The voltage across the capacitor is 0 volts. The voltage across the resistor is 0 volts. And since the capacitor is no longer discharging, the circuit amperage is 0 amps. You have completed this activity, discharging time constants of an RC circuit.