Science Buddies: "Ask an Expert"

We have the 6 volts of electricity, no problem. The basic stuff like, metal, rubber and wood are giving us the expected results. When we try to use saltwater it worked once, we cannot get any vegetable or fruit to conduct. This is killing me because I am following (I believe) everything properly. I do not know what I am doing wrong, I figured it would be easy as I did this exact experiemtn 30 years ago. Please help, do the wires matter? does one have to be copper and one zinc? why didi the saly water only work once? Plus the wire turned a copper color from silver.....I'm stumpped and my little girl is countin on me.

Hi

The wires have to be clean to get conductance. Vegetable oil will not conduct, and if the wires are covered with oil nothing may concuct. Is this the problem?Salty water will definitely conduct, so if it does not conduct for you either the wire electrodes have an insulating film on them or something in your apparatus has failed. It is notoriously hard to guess from a distance why an experiment does not work, so you are pretty much on your own to figure out what the problem is.

I wisih you luck!

Best regards,

Barrett L. Tomlinson

Hi lar0530,

It would also help if we knew what experiment you're doing. It sounds to me like you might be attempting a combination of these two:

https://www.sciencebuddies.org/science- ... p029.shtml
https://www.sciencebuddies.org/science- ... p018.shtml

which could be causing some problems:

Fruits and vegetables will produce a voltage (~1 V I think) when you connect one copper and one zinc nail, and this is because the different chemical reactions that go on at the surface of each metal inside the fruit create different potentials. However, they probably aren't able to produce very much current (net flow of electrons through the material). In fact, that experiment involves connecting a voltmeter, which is specifically designed with a large internal resistance to produce near-zero current for accurate voltage measurements.

In the other experiment, the voltage is supplied by the battery rather than the material you are testing -- you're just trying to see how much current will flow through the material.

Hope we can clear things up,
Amanda

Just a quick addition - when I've done conductivity experiments with salt water, the water often corrodes my wires, and they stop conducting. It sounds like this might have happened to you - if you have some sandpaper, try sanding the wires until they're the original color and try again. HTH.

Keith