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Electrolytic capacitors have 2 terminals of different length to indicate polarities, but ceramic capacitors have terminals of same length having no polarities. Why is there a difference between these two types of capacitors?

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You seem to answer your own question: because electrolytic capacitors are (unlike ceramic capacitors) polarized. – Phil Frost Aug 6 '14 at 16:27

Electrolytic capacitors will only work if they are connected the correct way round in a circuit. They are polarised, i.e. they are sensitive to the polarity of the applied voltage; the + connection of an electrolytic capacitor should be at a higher voltage than the - connection.

So the component needs to carry that information clearly. One of the mechanisms used is to have wires of different length, so that it is easy to get correct when using the component to manufacture something.

Ceramic capacitors are not sensitive to the polarity of the applied voltage, it doesn't matter which connection is more positive than the other. Hence there is nothing to indicate. Hence there is no need to have wires of different lengths.

Edited to incorporate helpful comments. The issue is for electrolytic capacitors is the voltage polarity across pins.

(Of course, adding wires of different length might cost a tiny bit more for the manufacturer, so they wouldn't want to do that for no reason :-)

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I would say that electrolytics (including tanalums) are sensitive to the polarity of the applied voltage, rather than to current flow. – Peter Bennett Aug 6 '14 at 15:28
I agree. Polarized caps can sink and source current without issue; if you think about it for a second it makes sense. To charge a cap current flows one way, and to discharge it the opposite. What good would a cap be if it could only go one way?! – ACD Aug 6 '14 at 15:36
Electrolytic capacitors pass AC current just fine, as long as the instantaneous voltage across them never changes sign. This is easily accomplished by applying an appropriate DC bias across them. – Dave Tweed Aug 6 '14 at 15:37
@Peter Bennett - Thank you. I was trying to avoid a self referential use of polarity and polarised. I hope my edit works okay. – gbulmer Aug 6 '14 at 15:40

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The construction of electrolytic capacitors makes them polarized because of the use of a paper soaked in electrolyte. As this polarization must be clear to the user, electrolytic capacitors have polarity markings on the case and different length leads.

Reversing the polarity can cause overheating and even explosion due to failure of the dielectric.

See this informative article for more details.

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@Andyaka "As this polarization must be clear to the user, electrolytic capacitors have polarity markings on the case and different length leads" – akellyirl Aug 6 '14 at 16:22
@Andyaka I know you know :) But that was a direct quote from my answer. I was pointing out that I have answered that in the answer. – akellyirl Aug 6 '14 at 16:25
I'm going blind!!! – Andy aka Aug 6 '14 at 16:27

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