why capacitors are used as filters?

Answer 1

The impedance of a capacitor varies inversely with the frequency; it has a high impedance at low frequencies, and a low impedance at high frequencies. When combined in a network with a resistor, the capacitor will produce a frequency-selective circuit, which is a filter. You can design both low-pass (attenuate highs) or high-pass (attenuate lows) with such a circuit.

Answer 2

A little math would make a good answer but most people reading here probably don't have a background in basic calculus.

A capacitor stores energy in the form of an electric field.

The current through a capacitor is proportional to the time rate of change in the voltage across the capacitor. This means that when a current flows through he capacitor the voltage changes as a charge builds up on the capacitor plates. The current has a cumulative effect on the voltage. This is the property that makes the capacitor useful in filters. A current in a given direction must persist to change the voltage.

The same property means that if the voltage across the capacitor is not changing there can be no current through the capacitor. This is what allows a capacitor to block DC.

Answer 3

We are talking about low pass filter, right? Then the impedance of the capacitor is lesser as the frequency becomes higher, so it will not allow the high frequency ac signal to pass into it. Especially, those of higher harmonics due to rectification process.

Answer 4

In rectifiers, the first stage is the conversion of bi-directional current into unidirectional current. This current is a fluctuating one. By the property of charging and discharging the capacitors smoothen the output voltage and current.

Answer 5

Widely capacitors are used to filter out A.C. current from D.C. current because of their ability to block dc and gives easy path to ac.
Capac. gives infinite resistance to dc but easily pass ac through them. That's why they are used as filters!