as I said before in recent science projects I have been studying the effect of water on the electrical resistance of materials that absorb water such as wood and sponge (the reason for the majority of my weird questions regarding water and electricity). I first tested wood but decided that wasn't a fair test due to the other chemicals in the wood, so here I am doing sponge as there are no chemicals in the material that affects how the water changes the resistance. As I said with the wood, I am calculating resistance by reading the current going through it at 9v, then dividing the voltage by current, and for the sponge, I got 87621 ohms. My question is would resistance stay the same as I go up the voltages to say 300 volts (I have no intention of testing it with that as I said lol) if not how much would it reduce by? I heard that the chemicals in the water may affect resistance as voltage goes up but would there be no space for that to happen in the water that is soaking an object due to the very low volume?

Specifically how much would the resistance change as I went up the voltage, as I have a common consensus that it will change, but by how much? This YouTuber in the video linked below did an experiment with high voltages, and whilst there is a reduction of resistance there isn't much... Is this roughly what I'd expect to happen in most circumstances with tap water and wet things soaked with tap water?



1 Answer 1


This is not straightforward. Here are one or two points to consider...

• The resistances that you find may depend more on the water trapped in convoluted channels in the permeable solid than on the solid itself. No doubt you are soaking the sponge in distilled water and squeezing it out several times, since you wish to avoid salts dissolving into the water that you use when measuring the resistance.

• You may find that the materials of the electrodes that you use to make your connections with the wet solid affect the resistance.

• The resistance that you measure may depend on the time for which your circuit has been connected. One reason for this could be build up on the electrodes of small gas bubbles or some other insulating product of electrolysis.

• I would not expect you to find Ohm's law to be obeyed accurately; in other words the resistance is unlikely to remain constant as you increase the voltage. One reason for this would be contamination of electrodes, as suggested earlier.

  • $\begingroup$ I am using tap water for this and I specifically have chosen sponge cos of there being no salts in the solid. What I am asking is how much do these things typically deviate from ohms law... $\endgroup$ Oct 5, 2022 at 14:02
  • $\begingroup$ "I am using tap water for this and I specifically have chosen sponge cos of there being no salts in the solid." Then I'd have thought that your results will tell you more about the tap water than about the sponge, which will surely act merely as a maze-like series of constrictions on the watery path through which charge can flow. Sorry that in my original answer I didn't take account of what you'd said about the sponge being free of soluble materials, and sorry that I'm unable to help with magnitude of deviation from Ohm's law. $\endgroup$ Oct 5, 2022 at 16:00

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