Its construction includes two conducting plates place near one another having vaccume in between them by which they are separated from each other. The medium which is used to separate these plate such as air or any insulator is called as dielectric. Usually the coducting plates are in the form of parallel plates. Therefore the capacitor is called as parallel plates capacitors.
When a voltage is applied to these plates in the form of a battery then a potential difference is establishes between the plates. The plate gains positive charge which which is connected with the positive terminal of the battery and the other plate gains negative charge because of the connection with the negative terminal of the battery.
The conducting plates are made of silver, copper or any other conducting meterial. The seperator medium is always an insulator.The positive charge is shown by +Q and the negative charge is shown by –Q.