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Its been a while since I posted here about what I have been trying to find out regarding resistance of water at high voltages. I may seem oddly obsessed with this, but it is forming a big part of a science project I am doing revolving around electrical safety with water and wet things, using detailed resistance values to back things up.

https://www.youtube.com/watch?v=3-3M3r69pOQ&t=332s

https://www.youtube.com/watch?v=MF9DCNkaE8I&t=335s

I've linked these videos before, but I have since studied them a fair bit more and calculated resistance values at different voltages as per the video with AC. Here is what I found;

Voltage (V) Resistance (ohms)
25 17000
49.8 171724
100 166666
150 166666
200 166666
225 164306
250 163265
287 163068

So for this I have come to the conclusion that whilst it doesn't quite follow ohms law, the resistance does not decrease by much at all (in the end only by like 8,000 ohms). My question is what would normally happen that it only strays from ohms law by a little bit, and what is the reason it strays from it but not by much? Also why does resistance remain at the same value for a bit? And would increased salts or any other substance in the water affect how much it deviates from ohms law?

Hope I have made the question clear and understandable :D

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  • $\begingroup$ What electrodes are you using? $\endgroup$
    – Chemomechanics
    Nov 12, 2022 at 21:21
  • $\begingroup$ physics.stackexchange.com/questions/487606/… $\endgroup$
    – Stevan V. Saban
    Nov 12, 2022 at 21:37
  • $\begingroup$ @Chemomechanics Its not me doing the experiment as I said its from a video but the guy attached wires to the metal/copper ends of a pipe $\endgroup$
    – effectivedragon
    Nov 13, 2022 at 4:47
  • $\begingroup$ @SteveSaban So basically that proves what I said about it being approximately but not quite ohmic? Been questioning this due to some saying its not ohmic $\endgroup$
    – effectivedragon
    Nov 13, 2022 at 4:48
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    $\begingroup$ @effectivedragon Technically, water is not a conductor so there is no reason for water to obey Ohms law. The ions in solution are the charge carriers and if the ion concentration (by addition of a salt or electrolyte) is high enough, the current will obey ohms law provided there is no other electrochemistry occurring at the electrode. $\endgroup$
    – Stevan V. Saban
    Nov 13, 2022 at 5:20

1 Answer 1

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Water is non-ohmic because when the voltage applied across the electrodes in the water (in order to create a current flow and thereby allow a resistance to be calculated) reaches a certain value, the water molecules begin dissociating into ions which contribute to the electrical conductivity of the bulk water.

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  • $\begingroup$ The thing is in this experiment cited rather than reaching a value and dipping the resistance kinda gradually goes down and not by much... seems theres a limit to how much the resistance decreases $\endgroup$
    – effectivedragon
    Nov 14, 2022 at 4:59

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