First of all, I have made two Leyden jars and connecting them together to get 2.272 nanofarad, I am trying to charge it using a twelve volts charger. When I measure how many volts it has when charging, using a multimeter, it shows me twelve volts, but when I disconnect the charger, it drops to three then goes crazy, I understand that it's discharging, I want to know why? And where the charges are going? I am trying to compare between it and an electrolytic capacitor except that it's not keeping the charge.
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$\begingroup$ There could be any number of things wrong with it; to answer this question, we'll almost certainly need more information about how the jars are constructed, how you're connecting them, etc. $\endgroup$– Michael SeifertCommented Mar 30, 2018 at 16:01
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$\begingroup$ I am using plastic bottles filled with water, and covered with foil, on top of it there is a nail. When measuring the capacity I am connecting one side of the multimeter with the nail, and the other with a thin cable connected to the foil. @MichaelSeifert $\endgroup$– Majed SaaeddinCommented Mar 30, 2018 at 16:15
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$\begingroup$ Whats the internal resistance of your multimeter? $\endgroup$– lalalaCommented Mar 30, 2018 at 16:57
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$\begingroup$ The multimeter is actually a resistor and provides a discharge path. Are you using distilled water? If not, then impurities in the water form a discharge path. $\endgroup$– Bill NCommented Apr 2, 2018 at 13:35
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1 Answer
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If the capacitance is really only $2.2\,nF$, that's not a lot. With that little capacitance, you can no longer treat the multimeter as having an infinite input impedance.
The voltage across a capacitor of $C$ farads discharging through a resistance of $R$ ohms will decrease with time as $$V(t)=V_0e^{-t/RC}\ \ .$$ So for example, if you're measuring the voltage across the $2.2\,nF$ capacitor with a multimeter with an input impedance of $10M\Omega$ (which is considered respectable), it will only take a tenth of a second for the voltage to drop from $12V$ all the way down to $0.13V$. My guess is that what's going wrong is simply that the Leyden jars are quickly discharging through the multimeter.
