Capacitor

Capacitors are basic component of electronics circuits.Capacitors store electric charge.There so many application where we use capacitor.Capacitor are used in timing circuit with resistor because they take time to fill with charge.They are also used in filter circuits because capacitor easily pass AC signals but they block DC signals.

Capacitance

This is a measure of capacitor's ability to store charge.Capacitance is measured in farads(F).

Capacitor Colour Code

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:

    brown, black, orange   means 10000pF = 10nF = 0.01µF.

                                                                         

Variable capacitors

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor.

 Note:Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.