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Crash Course Electronics/Capacitors (view source)
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Obviously metal plates don't care about polarity as they are almost identical and so can be interchanged without anyone noticing a difference. | Obviously metal plates don't care about polarity as they are almost identical and so can be interchanged without anyone noticing a difference. | ||
These were pretty large capacitors | These plate capacitors were physically pretty large capacitors but their capacitance is pretty low. | ||
To save space and increase capacitance the 2 plates can be made of metal foil and the air can be replaced by an electrically insulating layer | To save space and increase capacitance the 2 plates can be made of metal foil and the air can be replaced by an electrically insulating layer in between. To save even more space the foils can be rolled into a tube. ([http://wiki.4hv.org/index.php/Rolled_foil_capacitor_-_60_kV,_3.5_nF Insctruction] to create your own capacitor of foil) This cylindric form of foil capacitors was very common for a long time -but nowadays foil capacitors are mainly rectangularly shaped blocks. There are still few current foil capacitors which are cylindrical - but most of today's cylindrical capacitors are of an other kind (the elctrolytic capacitor, see next section about polarized capacitors). | ||
An other type of an unpolarized capacitor is the ceramic capacitor. Here the plates are insulated by ceramics instead of foil - increasing the capacity and maximum voltage rating. [ | An other type of an unpolarized capacitor is the ceramic capacitor. Here the plates are insulated by ceramics instead of foil - increasing the capacity and maximum voltage rating. [[wikipedia:Ceramic capacitor|Images on wikipedia]] | ||
=== capacitors where polarity matters === | === capacitors where polarity matters === | ||
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Capacitance varies when different materials are inserted or removed between the 2 plates of a capacitor. For example the capacitance increases when air is replaced by a dielectric (like the plastic foil of the foil capacitor or other insulators). | Capacitance varies when different materials are inserted or removed between the 2 plates of a capacitor. For example the capacitance increases when air is replaced by a dielectric (like the plastic foil of the foil capacitor or other insulators). | ||
In old radios variable capacitors with a rotary knob are found that look similar to a potentiometer. You can recognize plastic foils and thin metal plates which move when the knob is turned. ([ | In old radios variable capacitors with a rotary knob are found that look similar to a potentiometer. You can recognize plastic foils and thin metal plates which move when the knob is turned. ([[wikipedia:Variable capacitor|Example images on wikipedia]]) | ||
== Typical usage of Capacitors == | == Typical usage of Capacitors == | ||
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* Aging effects not as strong as electrolytics but more than film (brittle ceramics materials, can have water in the ceramic substrate) | * Aging effects not as strong as electrolytics but more than film (brittle ceramics materials, can have water in the ceramic substrate) | ||
* small piezo-electric effect: you can hear your audio or other signals in the capacitor at high frequencies and high voltage levels. | * small piezo-electric effect: you can hear your audio or other signals in the capacitor at high frequencies and high voltage levels. | ||
== Links == | |||
Calculate lowpass filter (using a capacitor and a resistor, german):<br> | |||
http://www.elektrotechnik-fachwissen.de/wechselstrom/rctp.php | |||
Measure capacitance using Arduino:<br> | |||
http://arduino.cc/it/Tutorial/CapacitanceMeter | |||
[[Category:Electronics]] | [[Category:Electronics]] | ||
[[Category:Martin Schied]] | [[Category:Martin Schied]] | ||