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Voltaic Cells

Introduces voltaic cells, the elements essential to their function and discusses how they are quantified.

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A Shocking Discovery - Voltaic Ancestors

Can the living become machines?

Credit: ace's photos
Source: http://www.flickr.com/photos/29289784@N02/8845910568/in/photolist-etFB2s-7EBFKt-cagECj-abFCbe-abJt4d-bVeC9J-bxjE4f-am56mT-bVNCQc-9wMKv6-9d8PTc-dZDmSE-axgiff-aRu87n-aRu7UK-awEXYZ-8obTz6-7xT3uT-bvzbsP-apmYUc-bf7JW6-cykSvN-7Dx2T1-ed7sQ8-dewWrb-8gDFVB-bhhWNk-aRwP3e-7CbGWh-7CbHxm-c1Bcrw
License: CC BY-NC 3.0


The voltaic cell has evolved greatly over time.  In the year 1780, the Italian physicist Luigi Galvani found that when you connected copper and zinc to the ends of a frog leg nerve, the leg contracts.  He called this animal electricty theory, which was really just his version of bioelectromagnetics.  The theory concluded that in the frog's legs was an electrical nerve liquid that reacted to a completed electrical circuit and caused the muscles of a dead frog to contract.

Wanting to challenge Galvani's animal electricity theory, Alessandro Volta built on Galvani's ideas and created the voltaic pile using only non-biological materals, thus reinforcing his metal-metal contact electricity theory.  Like Galvani, he had two metals to create his circuit.  However, he added a brined cloth into his invention.  Volta alternately stacked zinc and copper discs and put cloths soaked in brine in between the copper-zinc pairs.  The discs are like the electrodes in a voltaic cell and the brined cloth contained the electrolytes. 

But possibly predating both these inventions is the Baghdad battery, a group of artifacts created in Mesopotamia, during the dynasties of Parthian or Sassanid or Persian Empire period (the early centuries AD).  They were discovered near Baghdad, hence the name Baghdad batter.  Wilhelm König, the German director of the National Museum of Iraq, believes that the ancients may have used them as battery cells to electroplate gold onto silver objects.  Willard Gray recreated the battery by inferring that the copper and iron form an electrochemical couple and create voltage in the presence of an electrolyte.  In his experiment, Gray used grape juice to add electrolytes and proved that the Baghdad battery could very well be the first galvanic battery ever created and the long lost ancestor of the voltaic cell. 

Creative Applications 

  1. The Baghdad battery in theory is able to hold several volts. However, gas bubbles partially insulate the electrode and increases resistance. Why do the gas bubbles limit the possible voltage of the Baghdad battery?
  2. What differentiates the voltaic cell from Galvani’s first frog leg battery? What differentiates the voltaic cell from the voltaic pile? What differentiates the voltaic cell from the Baghdad battery?
  3. Do you think that Galvani’s animal electricity theory is legitimate? Is the metal-metal contact electricity theory legitimate?



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