Friday Sprog Blogging: circuitry.


Have you ever bought a present for a loved one where you weren't totally sure that he or she would be enthusiastic about the present, but you figured that you could always keep it if it was a dud?

I have this hunch that a good number of "educational" gifts that parents get for kids fit in this category.

I have a further hypothesis that the gifts that the parents are really secretly hoping that they will get to keep for their very own are the gifts their kids end up liking the most.

A recent data point in support of that hypothesis: The Snap Circuits set we got for the elder Free-Ride offspring's birthday this past summer.

After the Free-Ride offspring returned from fishing with Uncle Fishy last Sunday, we clamored around the Snap Circuits and took note of some concepts that are not obvious to kids who spend most of their time focused on macroscopic phenomenon.


Some ideas aren't too hard to get across, like the difference between an open circuit and a closed circuit. The fact that you are snapping in the connections to make a closed loop (or snapping them out to open it) conveys that pretty concretely. And elder offspring was quickly able to deduce that the same sort of thing must be going on in the switch component (where the opening and closing essentially happens in a black box -- I seem to recall the switches we used when playing with circuitry with my father were ones where you could see the connection being made or broken).

Harder to explain is just what it is that's moving through the circuit, and how that stuff behaves, and why it behaves that way.

The sprogs understand that the stuff that you get from the batteries is electricity, and we described it as electrons flowing through (or zipping around -- particle/wave duality, don't you know) the circuit. But I suspect they're still kind of fuzzy about just what these "electrons" are.

My better half tried to explain why the electrons would zip through the circuit in the first place, rather than just sitting tight in the batteries, by whipping out the multimeter.

Dr. Free-Ride's better half: Behold the multimeter, device of a thousand uses!

Uncle Fishy: Well ... at least three uses.

Dr. Free-Ride: And suddenly I'm in the mood for "wax lips".

Dr. Free-Ride's better half set the multimeter to measure potential differences and showed the sprogs the potential difference across the batteries. The strategy then was to compare the voltage difference to a potential energy difference for a book on the top bunk of the bunk-beds compared to the same book on the floor. (For some reason, the natural tendencies of physical objects on the top bunk are quite clear to the sprogs.)

Conveying the idea of resistance, for some reason, is a lot harder. In the circuit above, the light bulb lights up, by why isn't the motor turning?

We tried to explain how the current, passing through the light bulb, came out on the other end (on its way to the motor) somewhat diminished, so that there wasn't enough current available to make the motor go. Dr. Free-Ride's better half used a brief game of "mercy" to try to make the idea of (physical) resistance more concrete. And, we had a happy detour through the question of what makes the light bulb light up in the first place. (Hey, look at that little curly bit of wire between the two termini! When current goes through it, that wire glows. That wire has enough resistance that the current doesn't just zip through it, instead dissipating some of the energy as light and heat.)


When we removed the light bulb from the circuit, enough current got through that the little motor could turn. You can't see it in this picture (since the switch was in the open position as I snapped it), but when the motor turns, the plastic propeller sitting on top of it spins for a while and then lifts off and zips toward the ceiling before crashing to earth. And then, the children shriek in delight and you have to do it sixteen more times.

But in messing around with different ways to connect the components, we discovered that putting motor in the circuit the other way around, you get a fan rather than a flying saucer. This brought the sprogs face to face with the fact that current flows in a direction. Which direction the current is flowing through the motor affects which way the motor tuns when you flip the switch. And, there's a handedness to the plastic rotor, too -- and which way it's spinning (which is a consequence of the direction the motor is turning, naturally) determines whether it's trying to go upward or downward!

I probably should have broken out the molecular model kits right then to explain chirality.


Anyhow, my better half took the opportunity the other morning to connect some of these new ideas about electricity with a toy the sprogs have had for ages, a little chick that makes a chirping noise when you complete the circuit between the two little metal termini discreetly located on the chick's undercarriage.

The sprogs know how to complete this circuit themselves (the palm of one's hand does nicely), or with a friend (each puts a finger on a terminus, then you hold hands). But for the most part, they hadn't really thought about this as completing a circuit. (The also hadn't really thought much about humans as good conductors of electrical current.)

Dr. Free-Ride's better half: Are there any other ways we could complete the circuit and make the chick chirp?

Younger offspring: Wha?

Dr. Free-Ride's better half: What if I do this?


Of course, the chick chirped.

Younger offspring: Maybe there's electricity flowing from that part on your key that beeps and locks and unlocks the doors and that's why the chick is chirping.

You know, it's not the simplest explanation, but it's an interesting one. For sure, it's the kind of potential cause that you'd want to rule out to satisfy a clever six-year-old.

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When I was a kid, I once caught my dad working on my Lego present the night before my birthday.

The best kit I've seen so far that demonstrates electrical potentials and resistances is the one developed at Cornell (available at West Hill Biological Resources). It's essentially a water circuit system, with the added thrill that everyone gets wet if you don't hook things up properly.

You neglected to mention that, during discussion around current, when younger offspring was asked about other places where you might see currents the response was "currant berries!"

By Uncle Fishy (not verified) on 28 Sep 2007 #permalink

Remind me how the accounting is coming on whether U. Fishy is a net asset or liability in the process of educating the Sprogs. I'm sure he does get extra points for taking the Sprogs out sans parents to fishing, go to demo farms, etc.

I guess the confusion factor he tries to instill is just a reflection of some of the best H.S. learning experiences he had. AP Bio comes to mind, where the teacher, when pestered to answer a question she wanted the students to discover for themselves, would finally give one and then say "But remember I lie". That was a very effective way to develop critical thinking and learning.

By Super Sally (not verified) on 29 Sep 2007 #permalink

I have a couple of nits I would like to pick.

1) Noting really ZIPS through the circuit. Electrons flow surprisingly slowly through a circuit.

2) Current is most decidedly NOT diminished by flowing through a component. As a high school science teacher, that is a misconception that I battle against every single time I teach circuits. Kids seem to be obsessed with the idea that the current is "used up" by passing through a component. To combat this, a "pie van" model of electron flow is quite helpful. The electron (pie van) is loaded up with energy (pies) and then driven around the circuit (road). At the component (shop) the pie (energy) is unloaded, but the pie van (electron) keeps going round.

By Donalbain (not verified) on 29 Sep 2007 #permalink

My parents were academically gifted, but in the Humanties. They had English Lit degrees from Harvard and Northwestern, cum laude and magna cum laude. They could not answer questions of science and technology beyond elementary level. But, and this dates me, I learned electricity and electronics on my own by taking apart discarded radio and TV sets from street garbage, and building things from the components. Vacuum tubes, big hulking transformers, and the lovely color codes for resistors and capacitors.

In general, kids today lack access to individual components in this sense, and electronics retreates to magic by brand-named entities ("Intel in the box") packages in consumer products almost unimaginable from the 1950s, except by science fiction.

The kit that you described seems delightfully retro, and pedagogically sound.

My wife has taught this stuff, to (for instance) British folks studying for Electrical Engineering certificates, as well as to American teenagers in university labs getting a hands-on basis for elementary Physics and Physical Science.

Ohm's law is only an approximation, and is not hard-wired into our brains, but must be learned. And tactile, interactive, toy-like fun learning seems great to me. Please let us know how your sprogulation progresses.

You know, it's not the simplest explanation, but it's an interesting one. For sure, it's the kind of potential cause that you'd want to rule out to satisfy a clever six-year-old.

My seven year old cousin sprang a similar surprise on me a few weeks ago - we were rolling her "Thomas the Tank Engine" trains down a bridge and along a straight track, and we (read I) made the observation that one, only one of these, continually failed to make it off the end of the track (which was mildly undulating in the vertical plane to slow them down) and onto the carpet.

Me: "Why do you think that is?"

Her: "It's got too many wheels!"

So I explained about potential energy... how much energy they have depends on how high up they are at the start - all the same, in this case - and how much they weigh. And we got out the kitchen scales. They're not too accurate, but enough to determine that this carriage weighed the same as some of the others.

But it was indeed the only one with six wheels. I had to give her that one, so I explained about friction in the axles and against the ground, and how that wastes energy.

(Her two year old sister was scary - I showed her how to use the trains' pickup magnets to move one carriage with another without touching them and 24 hours later, she repeated the trick for me without prompting.)

By Justin Moretti (not verified) on 30 Sep 2007 #permalink

Wohooo! they have it both in Amazon and Target. I was looking for something like this for a friend's kid.

My nephews have these, they're pretty cool.

By David Harmon (not verified) on 24 Nov 2007 #permalink