Question

Why a capacitor blocks dc but permits ac.

Answer 1

What we know as electric current is rate of flow of charge per unit time what we express as dq/dt. What happens when we apply a voltage across the electrodes of a capacitor is, the dipoles present in the dielectic media is get polarised and this in the form of displacement current is established in the circuit. Even when a DC voltage is applied to a capacitor which is not charged a current will flow till the capacitor is fully charged as in the process of charging there exist dq/dt. once it is fully charged no additional charge is pumped in or out of the capacitor and it blocks current. In case of AC because of change in polarity of the applied voltage there will be continuous polarisation and depolarisation in each cycle causing rate of change of charge stored in the capacitor and hence flow of current with a 90 degree phase shift with the applied voltage. Please feel free if you need further clarifications.


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