A Homemade Lemon Battery John D. Worley and James Fwrnier St. Norbert College. De Pere, WI 54115 Years ago one of us (JW) took a course in graduate school on electrochemistry. Bernie Heston, who taught the course, was well known for his challenging examination questions. He always asked questions of a practical nature that forced us to apply the knowledge we had gained. Some of the focal points of hisquestions that I still recall, though 25 years have intervened, had to do with corrosion of ships' hulls, buried pipelines, and obstreperous fish tanks that had dissolving parts. The question I remember best, though, was his challenae to build a battery from items found in the household. f o r a number of yea& I have demonstrated t o students an answer to BH's question by plunging a galvanized nail into a lemon. By making a slit in the lemon and placing a penny in the slit, I have, using a voltmeter, shown the existence of a substantial voltage (-1 V). Our majors and nonmajors have been duly impressed hut have on occasion expressed disappointment that the homemade hattery could not do more than produce a voltage. One suggestion was to try to light a flashlight bulb from the battery. Relating my difficulties in this matter to one of our students (JF) in our General Chemistry course led to a suggestion from him that we try lighting an LED from six lemon batteries wired in series. We tried it, and sure enough, it worked. Still I was disappointed because the LED is so small it is difficult to see. Although the hattery could light a small bulb, we would surely fail the theatrical component of the demonstration. At this point J F suggested we wire into the circuit a capacitor from an old radio. By letting the capacitor charge up with power from the lemon batteries, we could touch thelead terminals from the capacitor to the leads on an ordinary
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Journal of Chemical Education
flash cube and set off the flash. The ever-cynical professor did not believe it would work. I t did. We demonstrated the system in front of our General Chemistry class. We found we had to wait a few seconds for the capacitor to charge up (about 30-60 s). As many cubes can he set off as desired. The effect is a little more dramatic if the lights in the room can be dimmed. I thought our students liked the demonstration. I t affords the instructor the opportunity to he concrete about such topics as anodes, cathodes, ions, polarity, voltage, and power.
Lemon battertes, wh~chare connected in s e m s to a capacitor setttng off a flash cube
