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February 26, 2014

Electronic Math classes

As the Electronics lab has become established I have started to take in kids from 6th and 7th grade for an Electronics class in one Math class a week. The kids have been pushing me to include some electronics in their 'curriculum' and when I found one of them in 7th grade trying to make a lemon battery in my class I could not let go of the opportunity. I usually take half the class and let the others continue with the worksheets with the Math teacher.

For the lemon battery they had a small piece of zinc that had been broken out off an old battery casing. They had wound it to a copper wire.

We talked about a new quantity voltage that gives in the water analogy the height of the water it is raised to and measured what we got from the lemon it was around 0.7 V. One kid was consistently able to find out which end is at a higher potential by putting the leads in their mouth. He said that the side he got the shock from was positive. I didn't try it out, but it was accurate every time I asked him.

We sawed through a battery carefully into two disposing off the material inside into a box and then flattening out the zinc plates. We then cut them into strips that we can use.

We talked about an LED and how unlike a light bulb it works only one way. Most kids have salvaged some LEDs from somewhere and are somewhat familiar with them. We started talking about ways (including the use of the multimeter) of figuring out which way it should be connected. We found four. The length of the leads (if available), the cut on the LED, the shape inside the LED and using a multimeter in the continuity setting. I then told them that they needed more than two 2V to light up an LED.

We used both his lemons and were still around 1.3 V still short of lighting the LED, as we had no other lemons I used a 1.5 V C battery in series. It got us to 2.8 V and enough to light the LED and light it did. Then we tried to squeeze out the lemon juice in bottle lids and were able to get enough voltage in four lids to light the LED.

I built on the experience with a few Xth grade kids as they created sets of wires with copper wire soldered on one side and a zinc plate on the other. I used this with the 6th graders. With 4 lemons and 6 kids it was fun exercise. They connected up two and when they hooked up the third the voltage went down. Then they started talking about negative numbers and remembered that the polarity is actually important and its otherwise like adding a negative number. I couldn't have come up with a better example of a negative decimal number than the one they created. I considered making a game of it, but the kids looked too serious to disturb so I let them at it till they got enough voltage to light the LED and look quite satisfied with themselves.

The other aspect that was easy to address was conversions from milli of a quantity to a whole e.g. mV -> V. This happens quite naturally as they try to interpret the results given from the multimeter based on the range they put it in.

I've also had a few lec-dems using an oscilloscope to explain the differences between AC and DC.

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