Although there was no Engineer in Residence (EIR) at my high school, I decided to use one of the hands-on activities from the EIR website. I was assisting in an SNC1L/2L class that was currently working on electrical circuits. This was a relatively small class composed of a diverse group of students that required a lot of individual attention when completing coursework. They were an overall great group of students to work with. With the correct guidance they worked hard to achieve their goals. They had covered the characteristics of electrical circuits and were about to cover the generation, measurement, and conversion of electricity. This seemed like an excellent opportunity to introduce the class the concept of fruit and potato batteries.
I devised a lesson plan that allowed the students to investigate the use of lemons, apples, and potatoes as batteries and to compare the measurements of volts and amperes to that of regular D cell batteries. It was a fairly easy activity to prepare for provided that the right materials were at hand. Most chemistry departments have copper and zinc electrodes that they use for the hydrolysis of water, I would advise using a wire brush to clean off any corrosion in order to improve conductivity. In addition you need a large supply of wires with alligator clips for setting up the circuits, and ammeters and voltmeters. Having something that requires low power to run like an LED light would be ideal as well. The final step requires a trip to the grocery store to acquire all the right ingredients. It is important to choose larger potatoes (like the ones used for baking) and other fruits since they can produce more electricity.
The lesson started with a discussion about the use of batteries in everyday life and how batteries work. The students then watched this video which does a great job of explaining batteries but was a bit too in depth for their level of understanding.
Prior to starting the investigation, the students practiced setting up circuits with ammeters and voltmeters. We were using the older style of meter, like the one shown below, which proved to be challenging because the students had to choose between reading off of three different scales. In the future I would try to get digital meters to make it easier for the students to interpret the readings.
The topic of using fruits and vegetables as batteries was brought up in class which certainly amazed the students and sparked some disbelief until they saw the potato clock. The key of course is the use of copper and zinc electrodes to create a path of least resistance for the passage of electrons.
The students were provided with the following handout and were sent to start their investigation.
The students were amazingly engaged in the lesson and the 75 minutes flew by! There were four stations set up and the students worked in groups of 2-3 to set up their batteries in series and take measurements. Although considerable voltages were measured from many of the fruit batteries, not enough power was generated to light up the light bulbs that we had. I would recommend getting LED lights for trying this activity so that the students can actually visualize the power that is being generated. This was a fun activity that I would definitely like to revisit in the future. This could definitely be expanded upon in a more advanced class to investigate how many potatoes you would need to create enough power for a toaster, or something along those lines. Discussing the practicality of using batteries for everyday living would also be a great conversation to have.
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