I Conductivity of saltwater dielectric vs current

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1. Aug 14, 2016

psuedoben

My partner and i have been running experiments for our research in micro algae separation, using a reactor containing aluminum electrodes. we run a 10v current across the electrodes, and flow saltwater between them. we were wondering how changing the conductivity of the saltwater might affect the current output, so we decided to test it. our hypothesis was that the higher the conductivity, the higher the resultant current. we thought this, because conductivity is measured as the inverse of resistance in a solution, and current can be written as I = V/R, so we figure if conductivity = 1/R, the higher the conductivity would mean the lower the resistance which would in turn translate to higher current. when running the experiments, however, we seemed to find the opposite affect. the current dropped rather linearly as we increased the conductivity of the water. do you think we were dealing with faulty equipment/procedure, or that our understanding of whats going on is flawed? wouldn't be terribly surprised if the answer is both.

2. Aug 14, 2016

Drakkith

Staff Emeritus
You're sure you increase the conductivity of the saltwater, not decreased it? How did you alter the water's conductivity? What electrical equipment did you use in your setup?

3. Aug 14, 2016

psuedoben

we measured the conductivity of the saltwater using a conductivity/pH measuring device. not sure of the brand or model. we increased the conductivity by increasing the concentration of the salt in the solution

4. Aug 14, 2016

psuedoben

We use an HP power supply unit

5. Aug 14, 2016

Drakkith

Staff Emeritus
Alright. How did you measure the current?

6. Aug 14, 2016

psuedoben

not sure of the model, if thats of concern i can check tomorrow when I'm next in the lab, but we use a current meter that is hooked up to the wires supplying the voltage

7. Aug 14, 2016

Drakkith

Staff Emeritus
Well, I'm not sure I can personally help you. I haven't performed this particular experiment before. If you haven't already, I'd be sure to double check everything, including your setup and measurements, and make sure you didn't make a simple mistake somewhere.

8. Aug 14, 2016

psuedoben

we'll be sure to do that, thanks! just out of curiosity, what would you personally expect to happen when the conductivity is increased?

9. Aug 14, 2016

Drakkith

Staff Emeritus
I'd expect your current to increase. Since you're supposedly keeping the applied voltage the same, increasing the conductivity decreases resistance which should increase the current according to Ohm's law.

Like I said, I'd double check everything and make sure you understand how your equipment works. I know I had issues in my physics class because we didn't know how the equipment was working and interacting with everything (especially the laptop we used). Once we realized what was going on we were able to correct for it.

10. Aug 14, 2016

davenn

that doesn't really answer Drakkith's Q

show us a drawing/photo of your setup ... you didn't really tell us how you connected the ammeter

Dave

11. Aug 14, 2016

Drakkith

Staff Emeritus
Indeed. This may be explained by having the ammeter in parallel instead of in series with the circuit.

12. Aug 15, 2016

psuedoben

awesome, thanks again. appreciate you taking your time to help. we'll be sure to spend some time focusing on the
I appreciate both of your help. i went in the lab today, and as embarrassing as this may sound, found that the issue was as simple as the batteries in the ammeter needing to be replaced..