Science Buddies: "Ask an Expert"

Hello experts! My Grade 5 kid is doing a science fair project on testing various pieces of metals (including aluminium foil, silver, copper, zinc and stainless steel, etc.) and to find out which one is the best electrical conductor. We have set up a series circuit with a 9V battery, a small light bulb and some thin copper wires. However, we cannot get a distinct result judging from the brightness of the light bulb when testing the metals. If we use a multimeter/ammeter to measure the current, will we be able to get some better results for comparison? We are grateful for your advice on how to get more precise results.

Yours sincerely ,
Mrs. Hoile

Yes! That sounds like a wonderful idea in order for you to have a quantitative analysis (with numerical data) in addition to a qualitative analysis (with observational data). Also, it's a good idea to have several trials for the conductivity of each material in order to then average those trials. (Having more trials is a way to increase the precision of data because it lowers the effect of random error.)

There are many articles about the use of a multimeter/ammeter, but below is one example that might help with the data collection.
Link: http://www.allaboutcircuits.com/textboo ... ter-usage/

-Kayli Masuda

ms3ttil - While this experiment sounds straight-forward, the problem is controlling the characteristics of your sample materials. For example, if all your samples were in the form of round wire, .01" in diameter and 3 feet long, your multimeter still might have a problem because of the low electrical resistance of the samples. They don't measure better than 1/10th ohm resolution, even on the lowest range, usually 0-200 ohms. I would guess that your examples consist of metal plates, wire, foil and other form factors. I don't see an easy way to get them into consistent forms that can easily be measured for conductivity comparisons. I would like to see the procedure the teacher is using to conduct the experiment. I agree with your observation, using a light bulb really won't differentiate much between the conductor samples you mention. At best, you could only see differences in conductors versus insulators. The materials you list are all relatively good conductors.

Rick Marz