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I thought I finally had a grasp on how ohm's law works but when I set up an actual experiment, the numbers don't match up. To keep a long story short, I converted a computer power supply into a lab power supply and I need a dummy load of some kind. I decided to try to build one. My first attempt was a nichrome coil at roughly 12ohms inside of a pvc pipe which I filled with plaster. It became dangerously hot after just a few minutes so back to the drawing board. As a temporary solution I decided to try electrolysis in an electrolyte solution of baking soda and water. This is where I must be calculating or doing something wrong. To test this load I used a laptop charger (19v). Using a multimeter I checked the resistance of the solution through the carbon rods I had suspended in the solution and got a reading of 4500 ohms (4.5 on 20k setting). When I wired the multimeter into the circuit to test amperage it showed roughly 3.3 amps... If V=I*R, the 19 volts divided 4500 ohms should only be .004 amps. How did I get 3.3 amps?? As I'm writing this question, I'm starting to think the laptop charger works on constant current, is that why? Or am I using ohms calculations wrong? Or what else is happening here? enter image description here

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Image 2 is the ohm reading. It shows 4.84 on the 2000k setting.

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  • \$\begingroup\$ Can you share a photo with the carbon rods and ammeter all wired up? 3.3 A seems very odd unless you accidentally touched the two electrodes together. \$\endgroup\$
    – The Photon
    Commented Jul 23, 2019 at 5:10
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    \$\begingroup\$ You measured an insulator that became a conductor in contact with the carbon rod and a chemical reaction between, So your results cannot compare to a different state. \$\endgroup\$
    – D.A.S.
    Commented Jul 23, 2019 at 5:23
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    \$\begingroup\$ I'm.. not sure if I'm puzzled or amused or perplexed, but at least curious about your choice of dummy loads. Normally you would use resistors, not random things mixed in random liquids. \$\endgroup\$
    – pipe
    Commented Jul 23, 2019 at 5:41
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    \$\begingroup\$ A useful dummy load is a car headlight bulb... 60W at 12V... A twin filament bulb gives 3 different resistance values... \$\endgroup\$
    – Solar Mike
    Commented Jul 23, 2019 at 6:40
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    \$\begingroup\$ There is no reason to assume that your electrolysis cell obeys Ohm's law \$\endgroup\$
    – Curd
    Commented Jul 23, 2019 at 9:43

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When you measure the resistance of your electrolyte solution with the multimeter, the meter applies a voltage of 2~3V to the sample and measures the current to calculate the resistance. But when you apply 19V to the sample, a chemical reaction will happen in your electrolyte solution, and the resistance will change. I think that's why the current increases to 3A.

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