# NEET Questions Solved

BOARD

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 ?                                                                                                                2mark

When an ideal capacitor is charged by dc battery, charge flows (momentarily) till the capacitor gets fully charged. When an ac source is connected then conduction current ${i}_{c}={\epsilon }_{0}\frac{dq}{dt}$ keep on flowing in the connecting wires.                                                                                               1/2mark

Due to changing current, 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.

1/2mark

Displacement current id is given by                                                   1/2mark

and is equal to the conduction current at all instants.                                           1/2mark

[Alternatively:  If the student explains the continuous flow of current, for a capacitor connected to an AC source, on the basis of capacitive reactance, or the charging and discharging of a capacitor, award 1 mark only.]

Difficulty Level:

• 92%
• 9%