capacitors working with ac and dc inputs

[anna essenker]

capacitors are said to resist changes in voltages,if so ...then why does a capacitor in a high pass filter allow ac input component and block the dc component.Ac voltages imply that the voltages vary with time.could anyone help me understand this...

 

[Audioguru]

A series capacitor couples AC but blocks DC so it is a highpass filter. A capacitor with a higher value can pass lower frequencies because it has a lower cutoff frequency.

A capacitor to ground is a parallel capacitor that resists changes in voltages so it is a lowpass filter that cuts high frequencies. A capacitor with a higher value produces a lower cutoff frequency.

 

[wighou]

Hi,

You are totally right, a capacitor resists changes in voltage. In other words, the capacitor try to keep constant the voltage between its input and output. Consequence: When a voltage vary with time at the input, the output voltage will vary in the same way to maintain the voltage drop constant between input and output. So the varying signal will be transmitted from input to output.
When the variations are not so quick, the capacitor have time to discharge (so, it does not maintain voltage difference between input and output). So, DC voltages is cutted between input and output.

 

[Y.SAI SARASWATHI]

I want to add little to previous post,
Capacitor mainly works with respect to potential difference between its two terminals,consider a parallel plate capacitor,whenever we apply some voltage(potential difference ) across it it develops electric field between 2 plates which will try to store charges based on its capacitance when we apply a dc voltage it never tries to discharge its stored charges to flow further (hence described as it stops dc)
when we apply an ac voltage for eg sinusoidal it continuously charges,when input sine starts decaying after a quarter cycle electric field will be in opposite direction hence it allows charges to flow(hence described as allows ac)