When an ideal capacitor is charged by a de battery, no current flows. However, when an ac source is used, the current flows continuously. How does one explain this, based on the concept of displacement current ?

When connected to a dc battery, no current flows as capacitor offers infinite resistance to d.c .Whereas since a capacitor offers finite resistance to a.c, current flows through it when connected to an ac source.

On connecting the capacitor to an ac source , the electric field across its plates changes continuosly. The displacement current arises due to the change of electric field between the two plates of capacitor.

Displacement current,