Experiment 5 is a fun one... using lemons to create your own battery to try and light up an LED. Definitely brings back memories of old kitchen table science experiments when I was younger...
I bought 2 lemons, cut them up into halves, and then proceeded to wire up three halves at first as shown on page 32. I took a voltage reading - about 1.4v. I then wired up my LED into the mix and... no luck. I tried about 3 other LEDs from the little bag I purchased, but none of them would give even a flicker. (It is very possible, as the author mentions, that these might not be low-current LEDs... even though I'm hitting the voltage, the current may not be enough to light 'em up.)
So, I tried to wire in the remaining half - two full lemons. I took another voltage reading... the meter kept moving between 1.5 and 1.6. The extra lemon was giving a slight boost in voltage, but would it light up an LED?
Again... no luck. But that's okay. I got the main point of the exercise which was to get a little better understanding of how batteries work. It's kinda cool to wire up four lemon halves with pennies and zinc-plated nails and get a voltage reading... any voltage reading. But 1.4 to 1.6 volts for 2 lemons? That's like a single 1.5v alkaline battery- just not as efficient apparently.
My other readings matched up with the author - almost 2mA of current and the resistance of each lemon half was around 25-35K when penny/nail were inserted very closely (same segment of lemon).
After letting the setup sit for about 15 minutes, I took some more readings... a slight decrease, so I imagine the lemon battery isn't going to last too long... of course, it is exposed to air (unlike real batteries) and I'm not using the cleanest nails and pennies for the experiment, so there's a lot of factors that are controlling voltage and current levels. Still, a fun experiment.
Just a few notes:
1. When inserting the nails and pennies, try to get them as close together as possible without touching... when I first inserted them on opposite ends of each lemon half, the voltage reading was down around .2 to .3... moving them to the same lemon segment AND about 1/4" apart really bumped up the voltage.
2. I may try this experiment again at a later date if I can locate some low-current LEDs... if anything, just to prove to myself that I wired it up correctly.
If any of my readers try this experiment and can get the LED lit up, please take a picture and send it to me - I'll try to post one or two of the first successful lightings.