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Webelos Adventures in Science requirements

Has anyone done this adventure with their den? I’m finding some of the info in the handbook & leader guide lacking.
My biggest question is about the lightbulb activity. One of the tasks is to see whether a parallel circuit or a series circuit runs down a battery faster. There is no information about what type of battery or bulb is recommended.
Does anyone know roughly how long to expect this to take? I would have thought that it would take longer than the duration of a meeting, but the leader guide has this listed as the last of three activities in the same meeting, suggesting that it’s actually pretty quick!
We’re doing this elective as a one-day event over school break next week, so we have time if we need it, but I’d like to know how much time to plan for.

Hi, @ChristyDryden,

We didn’t do this particular one, and I’m probably the wrong kind of engineer to do this calc, but I’ll dig around in my brain to see if any of my EE stuff is still in there. My estimate for duration might run something like this:

One AAA cell is about 750 mA-h at 1.5 V (nominal), so it’s roughly 1.5 V x 0.75 A-h = 1.125 W-h. So, a 1 Watt bulb runs (theoretically) for 1.125 hours (~68 minutes), assuming it could drain the cell entirely. It probably dims considerably before that point. For reference, one of those little E10 mini bulbs is about 1 Watt.

Use a higher wattage bulb (or multiple bulbs), and it should run out faster. The trick is that you won’t get much (if any) light out of a bulb that’s meant to operate at 120V from a couple of AAA alkaline cells because they typically have some activation or cutoff voltage to be able to push the circuit, so look for incandescent flashlight bulbs that will run at around 1.5V. You could run something with higher Voltage by putting the batteries in series (notes below), but I wouldn’t recommend aiming to generate 120V from alkaline batteries. :slightly_smiling_face:

An alkaline D-cell is between 10 A-h and 20 A-h, depending on the draw. A C-cell is about 6 A-h to 8 A-h. A AA alkaline cell is 2 A-h to 3 A-h. All of these cells operate at 1.5V nominal. Stick them in series (end-to-end), and you raise the Voltage of the resulting battery (~ linear sum of cell potential). However, you can only run until the weaker of the two batteries is “empty” as it were, so the A-h of the resulting battery is the same as the weaker battery. Two AA would give you 3V and 2-ish A-h. Connect the cells in parallel, and you get the same Voltage (1.5 V), but get the sum of the energies, so two AA in parallel would give you 4-ish A-h. I have a vague recollection that combining cells with drastically different energy storage (D-cell with a AAA for example) can have odd results, but I don’t recall if they were “dangerous” odd or “not easily predictable” odd.

I would say grab a flashlight bulb, a couple of batteries, and some wire, then test it out to get a duration and to see if the light is bright enough for you to tell the difference in a meaningful time frame. See if one of your den parents is an electrician, electrical engineer, or electronics hobbyist, who might have a multimeter. Then, the scouts could directly measure the remaining potential in the batteries to get an “exact” answer.

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Thanks - that was a lot of info!
I use a multimeter every day at work (and am sure we could borrow a couple) but my knowledge of principles behind what I do is very week.
I’m finding in general that the Webelos guide is a lot less thorough than the previous ranks. Which I guess shouldn’t be a surprise, since the handbook is quite a bit thicker than the younger kids, but the leader guides are all the same.

The Webelos program also recommends that you find guest experts to come in and teach the material. I know that’s not always practical, but that could be part of the thought process for less detail.

Hi,

I’m looking at doing this adventure with my den also. I’m still in the planning stage, but found this lesson plan that might give some ideas on how to construct the circuit: https://betterlesson.com/lesson/615545/series-and-parallel-circuits

There’s a link to a lab worksheet that lists out how to build the circuit, so hopefully that will help.

thanks,
Jill Wen

And here my first thought was:
How do I keep the scouts from growing bored while this experiment runs?

But… when I went to look at the requirements the resources I have handy all indicate the scouts need to simply build the two circuits. Now one could turn that into an experiment. In which case I would definitely have some activity to do while the bulbs get dimmer. (They only need to be enough to know one is more changed than the other.)

In case anyone isn’t sure what will happen, putting three bulbs in series will be dimmer but last much longer than three in parallel. I would make sure that they notice the trade-off if doing an experiment.

:man_facepalming: Thanks for pointing that out, @KirkWood. V = i x R: yet another reminder why it’s a good thing I stuck with structural engineering instead of electrical…

That’s true that the requirements simply say to build the circuits. But if the kids are following along in their handbooks, the section telling them to build the circuit then has a bunch of additional questions and tasks like figuring out how long the light lasts. At least a few of the kids will not find the activity satisfying if there are things we’re supposed to figure out and don’t.

The “guest expert” theory makes sense for some of the more focused adventures, but this one is all over the place. To accomplish Meeting #2 in the leader guide, we would need at least three guests to cover electricity, chemistry, and I forget if the third one was the solar system or playground physics!

In general, larger batteries (of the same variety) the longer they will last and in this case you don’t want them to last extra long.

I am actually happy I worked in civil/transportation engineering. Need a highway, bridge or railway let me know :slight_smile:

When I did this, I got a bunch of cheap bulb and battery holders. Makes it MUCH easier to hook the circuits together, when you just have to hook the wires together and don’t need to hold them against the terminals and whatnot. And you can re-use them next year. Here’s what I got, but use whatever you like:

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