# Capacitors in A.C.

## DC Capacitor - Recap

### A Capacitor is a device for storing Electrical Charge. A Capacitor consists of two parallel plates separated by an insulator. The symbol for a Capacitor is shown below :- ## Current in AC Circuits

### For the vast majority of Electrical components, the Frequency of an AC supply will have no effect on them. For example, the circuit below shows a resistor connected to an AC supply :- ### In the above circuit, if the Frequency of the the AC Supply is altered, the following graph will be plotted :- ## AC Current through a Diode

### In a Diode, the Current can only flow in one direction, giving a very different graph :- ## AC Current through a Capacitor

### If the Capacitor is connected to an AC supply, unlike DC, the charging of the Capacitor does not occur. This is because the constantly alternating supply will continuously switch between charging and discharging each plate. For example, the circuit below shows a Capacitor connected to an AC Supply:- ## AC Period > Charge time of Capacitor

### If the time taken for the AC signal to alternate is longer than the time to fully charge the capacitor, the following current graph will be generated :- ## AC Period < Charge time of Capacitor

### Low Frequency AC Supply :- ### High Frequency AC Supply :- ### If the Frequency of the the AC Supply is altered, the following graph will be plotted :- ## Capacitive Reactance

### It can be shown that the Capacitive Reactance, Capacitance and Frequency of an AC signal are related in the following formula :- 