Electrolyte challenge - same reading for all liquids

[rjharr70]

Hi,

We keep getting the same readings for all liquids in the experiment, tap water, distilled water, OJ and Gatorade. We have tried 2 different multimeters and different 9v batteries. All readings are in the .65 mA range give or take a hundredth. We rinse with tap water and 3 bowls of distilled water between each liquid.

One multimeter is a Commercial Electric model, the other is a Radio Shack. We set auto-range and 400mA ranges respectively.

http://www.homedepot.com/p/Commercial-E ... /205620380

https://www.radioshack.com/products/rad ... 5717078789

Any ideas what else we can do?

Thanks!

[HowardE]

Coincidentally I happen to have both of those meters too. 0.65mA is pretty low for a liquid that has conductive properties. If you have a resistor or two around you could try touching each of the leads to the coils on your sensor - completing the circuit with a resistor instead of a liquid. You should see current on the meter and you can use Ohm's law to verify that the current reading is in the right ballpark.

Another option is to try a liquid guaranteed to conduct - saltwater. I found an experiment on the web that uses a similar setup to demonstrate that saltwater conducts electricity. http://www.hometrainingtools.com/a/salt ... it-project has students make electrodes, show that water alone won't conduct enough to light a bulb but that the addition of salt will cause the bulb to light. They lit a bulb with 9V by mixing 1 tsp of salt in one cup of water. Flashlight bulbs of that type will draw between 60 and 200 mA which is plenty to register on your meter. If you mixed salt water in that concentration and tested it with your setup you should be able to confirm that everything else is right or determine that you have some other problem.

Howard

[rjharr70]

Thank you very much for your quick response Howard.

My wife's coworker wondered if the multimeters that I was using were not sensitive enough, so on the way home from work, I picked up a less expensive multimeter. It had a 200mA DC setting. It produced readings that were fairly consistent with some others who have conducted this experiment. My son was happy and I was very relieved!

Thanks again!
Rich

[knaegeli]

We having the same problem! .68 for all liquids! We used the same Radio Shack multimeter mentioned above. Can you explain why we may be having the same problem with the same multimeter and a fairly similar reading?

I would think that a more expensive multimeter might be more trustworthy, rather than less!

Thank you!
Katie