A capacitor is a discrete component that can store an electrical charge. The larger the capacitance the more charge it can store.

The unit of measurement of capacitance is the farad. Often you will see capacitors of much less than a farad. These will be measured in microfarads (one millionth of a farad or 1/1,000,000) or picofarads (one million-millionth of a farad or 1/1,000,000,000,000).

There are two types of capacitor:

• polarized or electrolytic capacitors
• non-polarized or non-electrolytic capacitors

Polarized capacitors

• These generally have larger capacitance values. Polarized capacitors have a positive pole and a negative pole, so they must be connected to a circuit the correct way round.

Non-polarized capacitors

• These are usually much smaller than the polarised type, and have smaller capacitance values. These might range from a few picofarads to a few microfarads. They don't have positive or negative poles so they can be connected to a circuit either way round.

Applications of capacitors

Capacitors are used to smooth rectified alternating-current voltages into steady direct-current voltages. They can also be used to filter out fluctuations in a signal.

Capacitors are often used in series with resistors to achieve a time delay. The time it takes for the capacitor to become charged is related to the size of the capacitor and the value of the regulating resistor.

 Exercise 26.Convert these values to Farads as in the example. Check answers with your partner.
Example: 33 nF = 0.000000033 F = 33·10-9 F
a) 100 pF =
b) 10 μF =
c) 0.1 μF =
d) 68 nF =

 Exercise 27. Read the text and then answer the questions below.

The small capacitance capacitors are made of polyester (nF) and ceramic (pF). For large capacity values (μF) electrolytic capacitors are used. These are polarised and marked with the maximum voltage. Be careful not to connect electrolytic capacitors the wrong way or across a higher voltage.

What kind of capacitor is this?                                   
It’s an e........................ c...............................
Describe its characteristics?
Its value ........................................................and ............................................................Volts. It can work until ..........................ºC

 Exercise 28. Discuss with your partner what will happen if we use them in a 50V circuit.