Capacitor and esistor in an ac circuit.

  What happens if a capactor were added to the resistor in the ac circuit that was discussed in the previousw section? Now currents flowing through the resistor would lead to charging and discharging the capacitor, so unlike the voltage V_R across the resistor the voltage V_C across the capacitor would no longer be maximized when the current is maximized. In fact, the voltages across the capacitor and resistor are 90 degrees out of phase, with the V_C lagging behind V_R (or the current). As can be seen in the applet below, it is clear that the applied voltage V_app is simply the vector sum of V_R and V_C. Click on the "Show Current" button in the applet below to see the current flowing in this circuit.

  Since the impedance of a capacitor depends on the driving frequency, V_C will change, which in turn will change the amount that V_C lags behind the applied voltage, when the driving frequency changes. Try changing the frequency in the applet below.

Use the above simulation to answer the following questions:

What is happening when the direction of the current is opposite to the applied voltage?