how do blocking capacitors work?

Question

blocking direct current and allowing alternating current

Answer 1

With DC acfross a capacitor, the cap simply charges to the dc value and nothing more happens. WHEN A.C.is applied, the capacitor looks like a low impedance. As the charge changes on one plate the other plate follows suit and ac current flows.

Added: A capacitor is a linear element it cannot clamp

Answer 2

The flow of current through the capacitor is not due to conduction - as in case of metals. It is the alternate charging and discharging of capacitor's plate which gives apparant current called displacement current in AC since the voltage is also changing direction periodically.

However, dc does not change the direction and hence capacitor can not conduct. In a capacitor, there is an insulating material between the plate called dielectric.

Blocking capacitor is put in circuit to block dc and allow ac to pass through it.

Answer 3

To DC, a 'cap' appears as an 'open'. Once the cap charges to the battery (or DC supply) all current-flow ceases.

With AC, the cap is in a constant state of 'charging'. First in one direction, and then the other, 'alternating' with the AC supply. As such the cap appears to always be letting current flow because of this, but its rate of charge causes an impedence in the circuit.

In circuits where you may want to pass a high frequency signal as opposed to a lower frequency signal, you use a cap along with a resistor in such a way as to create a filter, which can permit, or block frequencies of almost any desired range you wish. I believe there are filter designs on chips which are a little more complicated but they are more accurate as to where the cut-offs are for frequencies that can pass and those which cannot.

Answer 4

With DC the plates in the capacitor get full an stop taking any more charge.
with AC when the polarity reverses the plates discharge then fill up to capacity (The positively charged plate now negatively charged) until discharging again when polarity reverses. The ideal capacitor to use is one where it almost fills up between reversals. If it does fill up you get signal clipping.