The most common used type of capacitors used will be of parallel plate type. If only two plates are used for the capacitor, there are will be disproportionately large to obtain large vales of capacitance. In practice therefore, the construction of parallel plate capacitor have a large number of parallel plates, as shown in fig.1 the odd numbered plates(metal sheet) are being connected in parallel and taken to one point(A) & the even number of plates connected in parallel and taken to other point(B). The value of the capacitance obtained can be increased by changing or using different dielectric as medium between plates instead of only air. Fig. 1 shows capacitor having metal sheets which are separated by dielectric. Connection are brought out at point A and point B as shown. The dielectric used may be glass, or mica, or Paraffin paper. The paraffin papers can be used for cheaper construction. The value of capacitance obtained is fixed depending on the parameters of plates, the dielectric and distance of separation.
Now the Fig. 2 shows the construction of a papers insulated capacitor. This is quite easy. It consist of long strip of aluminium foil or tin foil which is separated by a thin dielectric such as paraffin paper. The dotted line shown in fig. 2 is dielectric and the other solid is the conductor (aluminium foil). The strips are rolled up spirally. The whole material is soaked in metal paraffin was which sets solid on cooling
For use of capacitors on high voltages, smaller units are made as described and later these units are connected in series parallel combination as required, thus making large size units.
For capacitors whose value should be capable of varying as suitable, they are constructed as parallel plate capacitors with a number of parallel sets of vanes, one set being fixed and other capable of moving their position relative to the fixed vanes. The dielectric used is air as medium between the vanes. By changing the position of moving vanes with respect to fixed vanes, the value of the capacitance can be varied within designed limitation.