Archive for April 15th, 2009
It’s not about being politically correct. Limes are cheaper than lemons. A bag of 5 limes was $1, lemons were $2. Since we were sticking metal in them and then throwing them away, frugality wins. Besides, I have some leftovers that may become margaritas.
Now, I ran out of time and didn’t create a lab sheet, so I had to wing this a bit. We did have a kit from Carolina that included electrodes of Fe, Cu, Al, and Zn. I decided I would have less trouble if I did the cutting into the limes. I used a plastic knife and cut two slits about 3/4″ apart, large enough for the electrodes to easily slip into the lime.
On the board I created a simple 4×4 matrix of the metals and had the students test each metal pair as electrodes. I also had them test Fe-Fe, and Cu-Cu, etc. That meant they had to share electrodes to get the similar pairs. They found that only dissimilar metals created a voltage and the voltages were not all equal. Cu-Zn created the largest, at around .9 volts.
Next, I had them pull out change from their pockets and try the coins as electrodes. I also had some galvanized screws (zinc coating) for them to use.
Once they had a feel for what makes their battery work, I gave them each an LED for them to try to light up. A single battery didn’t have enough voltage, so they had to partner up with another group and figure out (with some guidance in the form of a drawing on the board) how to wire the batteries in series. With two, they could get a red LED to light up. We had to turn out the lights to make it visible. The green LEDs seem to require more power and didn’t light up with the same batteries. They also wired three together and made the light even brighter.
Yes, I needed more organization. Tomorrow we do series and parallel circuits using switches and light bulbs. It’s fourth quarter and I feel like I’m out of energy myself.