Conductivity of saltwater dielectric vs current

[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 what's going on is flawed? wouldn't be terribly surprised if the answer is both.

 

[Drakkith]

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?

 

[psuedoben]

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?

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

 

[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

We use an HP power supply unit

 

[Drakkith]

Alright. How did you measure the current?

 

[psuedoben]

Alright. How did you measure the current?

not sure of the model, if that's 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

 

[Drakkith]

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.

 

[psuedoben]

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.

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

 

[Drakkith]

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.

 

[davenn]

not sure of the model, if that's 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

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 ammeterDave

 

[Drakkith]

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

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

 

[psuedoben]

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.

awesome, thanks again. appreciate you taking your time to help. we'll be sure to spend some time focusing on the

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.

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..