Ask A Scientist© Physics Archive

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.
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Answer:  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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