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Question:
My 8 year old son recently did a science experiment using an electrical kit from Radio Shack. In it he showed how different materials were conductors or non-conductors. We were all amazed that a banana showed conductivity. How and why. Other fruit and vegetables, only a few, did not. Th anks.



Replies:
I am also a bit surprised that a banana conducts electricity but I think I can explain why, in general terms. You can think of a banana, or most fruits, as being mostly water and its electrical conductivity will be related to conductivity of water solutions. You probably also did an experiment with water and various things (such as sugar and salt) dissolved in it. Some solutions conduct and others do not. Those that do form ions in solution, for example salt is sodium chloride (NaCl) and, because of the properties of salt and water (a polar solvent), dissolves as Na+ (sodium atom missing one electron) and Cl- (chlorine atom with an extra electron -- chloride ion). Once in solution with many other Na+ and Cl- ions around the individual ions are free to move around in the solution, independent of one another. When you measure the conductivity of the solution you are applying an electric potential, positive charge at one electrode and negative charge at the other. The positively charged ions will be attracted to the negatively charged electrode and the negatively charged ions will be attracted to the positively charged electrode. When a negative ion reaches the positive electrode it deposits its electron in the electrode, the electron travels through the meter and appears at the negatively charged electrode to move onto the positively charged ion, neutralizing it. Salts & acids form ionic solutions so fruits like oranges (citric acid) and bananas (potassium salts??) can conduct in this manner.
Hope this helped.

Greg



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