QUESTION #21

# Why does a high frquency pass through a capacitor and a low frequency doesen't?

Asked by: Kevin Ocampo

### Answer

A capacitor is essentially two conductors separated by a dielectric (INSULATOR). Therefore, current does not pass through a capacitor but a result equivalent to it passing through can be obtained if the current is alternating [AC] (as opposed to direct [DC].)

Alternating current reverses its direction with a given frequency, f (which can change as a function of time). The result is that the polarity of the potential voltage as measured at the input terminal of the capacitor swings from positive to negative values of the voltage.

When the applied voltage goes negative,electrons are stored on the capacitor plate to which the voltage is applied and since like charges repel,electrons are forced off the other plate of the capacitor. Then when the applied voltage goes positive electrons are pulled off this plate and it becomes charged positive and this attracts electrons to the opposite plate.The opposition to this action is called capacitive reactance further classified with resistance and inductive reactance as impedance.Capacitive Reactance in ohms=1 divided by the product of the capacitance in farads multiplied by the frequency in cycles per second.As you can see,the reactance will decrease when either or both the frequency or the capacity increases.
Answered by: Joe Thomas