Electrolyte Challenge Experiment

[deleted-306420]

There is an inconsistency in the website regarding the electrolyte challenge experiment. In the description of the procedure and the diagram of the circuit, the positive terminal of the multimeter is connected to the NEGATIVE terminal of the 9V battery. However, in the photos of the setup and the FAQ section, the positive terminal of the multimeter appears to be connected to the POSITIVE terminal of the 9V battery.

Which is correct?

[deleted-71588]

The circuit diagram is correct if you want the meter reading to show positive numbers when current is flowing. For digital meters on voltage and current scales, the only thing that happens if you reverse the leads is you get a negative instead of positive reading.

[deleted-306420]

Your answer is the opposite of what is says in the FAQs on the website, which says:
"Q: What if I am getting negative numbers for my results?
A: If your data is negative, make sure that your connections are correct. The POSITIVE node of the battery should be attached to the red wire (+) from the multimeter. If you have a negative connected to a positive (for example, a black wire connected to a positive node on the battery), it will reverse the polarity and give you negative data."

Which causes a negative reading? ++ or +- ?

The circuit diagram says to connect + to -, but the photos and FAQ say + to +.

Right now we have not been able to get any readings above 0.0, and are getting a new multimeter. But we want to make sure we are clear on all other aspects of the setup to avoid further delays.

[rmarz]

vlee - A digital multimeter will read out correctly when the battery (+) is connected to the meter (+). The attached diagram is not correct. The magnitude of current will be measured accurately, but the display will show a (-) before the value. Your experiment is still valid whether the meter is reversed or not. A moving coil analog meter will force the needle to the stop in the negative direction, with no readable value. More concerning is that you are not getting any reading. Have you set the proper range on the meter? Typically, this might be the 0-20 or 0-200 DC milliamps range for conductive liquids.

Rick Marz

[deleted-93346]

I'll second Rick's reply. In a loop of devices that drop voltage, each passive device must be in the (+) -> (-) orientation with respect to the current flow, but batteries are reversed in polarity since they have a voltage gain rather than a drop. Going around the loop all the voltages must sum to zero.