Sunday, April 5, 2015

Fruit and Vegetable battery

Hello there. I've seen a lot of lemon battery projects, potato battery projects, etc. on Youtube, but when I tried them on my own, it seldom works the way they do on youtube, online, or in science books I've purchased. So, I tried to work out as many kinks as possible, but I still encountered some glitches. 

I've done this project in the fall of 2014, but I didn't blog about it for two reasons. Firstly, I didn't take my own photos in the classrooms. Secondly, the kids loved the experiment because it was brand new to all of them, but I found it stressful and frustrating. I was conducting the project for the first time, and I didn't know what to expect. 

Still, this one is definitely worth a try.

Supplies you need -
  • pennies (anything copper is fine, too)
  • galvanized nails (zinc covered)
  • alligator clips (buy these at Harbor Freight, Frys, etc.)
  • multi-meter (again from Harbor Freight, Frys, etc. You can get them from free from Harbor Freight with coupons.)
  • assorted Resistors  > 500 ohms (Harbor Freight, Frys, or excess electronics shops)
  • assorted LED's (Harbor Freight, Frys, or excess electronics shops)
  • assorted fruits and vegetables 
  • plastic knife
  • 9 volt battery
The science project I've designed for the elementary school is as follows - the students need to figure out at what voltage each of the LED's (amber, red, yellow, green, and blue) light up. 

I was told that amber LED should light up at 2 volts, red LED at 3 volts, and yellow, green and blue should light up at 4 or 5, but this was not the case for me.

Summary of project instructions -

  1. Create a fruit/vegetable battery by poking one nail into the one end of the fruit/vegetable and inserting a penny into the other end of the same fruit/vegetable. If the fruit/vegetable skin is tough, use the plastic knife to make an incision to insert the penny.
  2. Connect an alligator clip on the nail and another on the penny.
  3. Connect a multi-meter to the other side of alligator clips, measure the voltage and write it down.
  4. After unclipping the alligator clips to the multi-meter, clip them to a LED and see if the LED lights up. If it does light up, write down the LED color next to the voltage.
  5. Go on to the next LED. If it doesn’t light up, connect another fruit/vegetable battery to the circuit by repeating from step 1.

My classroom findings are (ranging from 2nd graders to 5th graders):
  1. The alligator clips I purchased were too small for younger students.
  2. The alligator clips get slippery with fruit/vegetable juice, which makes them even harder to use.
  3. The LEDs I purchased (some inexpensive ones from Excess Solutions as well as some quite expensive ones from Fry's) didn't light up at expected voltages. The LEDs started lighting up ~7 volts.
  4. To get 7 volts of voltage, most teams of students had to string ~10 fruits/vegetables.
  5. The LEDs were supposed to light up at different voltages, but several of them lit up ~7 volts, but some of them were quite hard to see or were directional.
The LEDs didn't light up at expected voltages due to inefficiencies in the circuit. A voltage reading could be affected by how the clips were clipped to the nail or penny.

I have a 9 volt battery and assorted resistors listed in the supplies list, because if you're not sure if the LEDs are working or not, you can always test them by hooking it up to the battery.
  1. Clip an alligator clip to left side of the battery and clip another alligator clip to the right side of the battery.
  2. Clip one end of the resistor to one of the alligator clips.
  3. Clip another alligator clip to the other end of a resistor.
  4. Clip a LED between the alligator clips from the left side and the right side, making a closed loop. If the LED lights up, then LED is good. If not, go on and test another one.
  5. Then use the tested LED to test your fruit and vegetable battery.

I was conducting this experiment in a 2nd grade classroom, and it was very stressful because younger students had more difficult time working with the alligator clips. Everyone was asking me to help with clipping, and there were only two adults (me and the teacher) in the classroom. I was muttering to myself that I'll never do this project again when a little girl came up to me and said, "This experiment is so awesome! I never thought you can light up a light bulb with a cucumber!"

Her team had a series of potatoes, lemons, cucumbers, etc., but that comment just made my day. She didn't see how I was stressed out because it wasn't working the way I had planned, but she only saw how neat it was to light up a LED with fruits and vegetables.

Though most students struggled to light a LED, they were very enthusiastic and really pushed themselves to get the most out of the experiment. I plan to do some variation of this project in the future; however, I'll ask for a volunteer help from each classroom.

A picture of the electronics kit I created for this project.

Again, though I was stressed out by this project, it got progressively better with each class (probably because I tossed out my worksheet and just went with the flow). Every class enjoyed this project a lot and asked me if we had another electronics experiment in out project list for this year. 

There is an experiment with conductive dough. I might give that a try soon, and let you know how it goes. In the mean time, why don't you give this one a try?

Have fun.