Question

When an ideal capacitor is charged by a dc 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?

Answer 1

Ideal capacitor means infinite resistance for dc. When an ac source is used, the current flows continuously, but we know that the capacitor has dielectric (air) between its plates. So, ideally there is no current, and circuit would be incomplete. In real capacitor is charged due to contribution of varying electric field. The current between the capacitor plates is given by displacement currentD = ∈ E

Answer 2

Hey !!

When an ideal capacitor by a dc battery, the charge flows (momentarily) till the capacitor gets fully charged. When an ac source is connected then conduction current ''ic = dq/dt'' keeps on flowing in the connecting wires.

          Due to changing current, the charge deposited on the plates of the capacitor changes with time. This causes change in electric field between the plates of the capacitor which causes the electric flux to change and gives rise to a displacement current in the region between the plates of the capacitor.

Displacement current is given by Id

                      Id = ε₀ dΦe / dt

and is equal to the conduction current at all instants.

GOOD LUCK !!