Capacitors and Capacitance


Capacitors are probably the most important part of basic electronics, they are not actually hard to understand. Then can be found in Tuned Circuits and many filters too. Capacitors are in most circumstances formed by two metal plates on each side of an insulator, this insulator is known as the ‘dielectric’. See the electronic symbols below.capacitor-symbols

The ones you need to know for the Intermediate licence are Fixed, polarized, pre-set and variable, the rest are included here for reference.


How does a Capacitor work?


First thing to remember is that Capacitors BLOCK DC Current only allowing AC Current to pass. Because the plates of the capacitor are seperated by an insulator when power is supplied to the capacitor this allows one side of the capacitor to fill, when its full the AC current jumps the insulator allowing the current to flow on. Remember that Capacitors STORE ENERGY! anything that stores energy can give you a nasty shock!. Some capacitors are polarised and as such need to be fitted the right way round otherwise they may well explode. Polarised Capacitors are called ‘Electrolytic’ capacitors


The insulating material between the plates can be Ceramic, polystyrene, polyester and air, there are also other materials used.




Unit Unit Name Division of Units
1F Farad 1,000 mF
1mF MilliFarad 1,000 µF
1µF MicroFarad 1,000 nf
1pF PicoFarad


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