Question

Explain why current flows through an ideal capacitor when it is connected to an a.c. source but not when it is connected to a d.c. source in a steady state.

Answer 1

A capacitor is a device that stores electrical energy in an electric field.The effect of a capacitor is called capacitance. An ideal capacitor is defined as a purely reactive device and has an absolute zero resistive effect.

Complete step by step answer:
When an ideal capacitor is charged by a DC battery, the charge will temporarily flow until the capacitor is fully charged. An ideal capacitor means infinite resistance to direct current.When an AC source is connected to the condenser, conduction current, $\;{i_c} = \dfrac{{dq}}{{dt}}$ the driving current continuously flows on the connection cable.

Due to the changing current, the load deposited in the condenser plates changes over time. This causes the electrical field modification between the condenser plates which changes the electrical flow and gives rise to the movement current in the region between the condenser plates.The displacement current is given by, ${i_d} = { \in _0}\dfrac{{d{\varphi _E}}}{{dt}}$.

Note: An ideal capacitor has infinite resistance when connected to direct current. When used with an AC power supply, the current flows continuously; ideally, without current, the circuit is incomplete as we know there is a dielectric between the plates of the capacitor. Therefore, due to the contribution of the changing electric field, the real capacitor is charged. The current between the capacitor plates results from the displacement current.