Disclaimer:

Reprinted by permission of Dick Berg, University of Maryland, for use on this website.

The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources.

Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA.

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NOTE: The single 1 farad capacitor takes at least 20 minutes to charge and will run the motor about 50 seconds, whereas the 4 capacitors in series (250,000 microfarads) takes less than 10 minutes to charge but will run the motor for only 15 seconds. CHOOSE THE ONE APPROPRIATE FOR YOUR SITUATION. 

NOTE:   For best operation of the lemon roll it on a table while pressing on it to break up some of the tissue cells on the inside.  A fresh lemon will give a voltage reading of about .89 volts when used in this manner.  With time (approximately 24 hours) this voltage reading will rise to about .98 volts.  This is due mainly to the dissolution of some of the electrode material into the lemon tissue, as observed by the blue and black areas that develop around the electrodes.  The higher the voltage, the better this demonstration work so it is advantageous to get the higher voltage without the waiting period.  To do this inject 2cc. of saturated Copper Sulfate solution into the middle of the lemon.  This step simulates the dissolution of the copper electrode into the lemon tissue.  Again roll the lemon to disperse the copper sulfate throughout the lemon tissue.  Now the fresh lemon will develop the .98 volts without the waiting period.  Using a copper and Mg electrode will give approx.  1.5 to 1.6 volts for the lemon battery and therefore reduce the charging time.  

While you can not usually run motors and lights directly off of the lemon, a low-voltage low-current  Piezo buzzer works quite nicely.