Why does a capacitor block DC and not AC?

Answer 1

A capacitor consists of two plates separated from one another by an insulator. These plates are normally thin foil and can be sandwiched around a very thin insulator and wrapped into a small package. Since there is an insulator between the plates, DC connected to the two plates cannot flow as long as you do not exceed the breakdown voltage of the insulator. AC current is a different story. Because the insulator is very thin and the effective plate area is relatively large, a negative charge building up on one plate causes electrons to be repelled from the opposite plate, and as the charge on the first plate reverses and becomes positive, the electrons in the opposite plate are attracted back again. This results in a matching alternating current flow on the opposite side of the capacitor.

actually what happens, capacitor provides a reactance to current.

Xc= 1/ (2*pi*f*c) ,where pi=3.14, f=frequency , c=capacitance vaue

as dc current is independent of frequency so Xc becomes infinite so dc current gets infinite resistance. so it is blocked

Answer 2

A capacitor is made up of two plates with a insulator between them, this means that these is no physical path between the two plate, this means DC does not flow. When you connect a changing supply it creates a changing magnetic field, this induces an emf into the other plate allow AC to 'flow'

Answer 3

because dc voltage flows only in one direction and ac voltage oscillates ,and is more efficient

Answer

Because, for d.c., after an initial 'charging current', the voltage across a capacitor is equal and opposite that of the d.c. applied voltage. This means the net voltage in the circuit is zero and no current can flow.

For a.c., for each half-cycle, the applied voltage reverses direction before the capacitor can fully charge. So the applied voltage is always greater than the opposing voltage offered by the capacitor, allowing current to flow. This process repeats itself every half cycle. So while the capacitor will not prevent a.c. current from flowing, it does offer a certain amount of opposition which we call 'capacitive reactance'.

Answer 4

When DC is applied to a capacitor a current flows for a short time until the capacitor is charged, with positive charges on one plate and negative on the other (a current is a movement of charge).

Therefore, for a short time before it is fully charged, a capacitor does conduct current.

When AC is applied to a capacitor, it allows current to pass alternately forward and back as charge flows into the plates and out again. So, seen from outside, current is flowing.

Answer 5

impedance of capacitor is 1/(2 3.1416 f c). as direct current has no frequency impedance of capacitor becomes infinity and it will not allow direct current flow through it