electricity – Page 3 – Montessori Muddle

Insects with solar cells

Insect_in_Lindos_Rhodes — The yellow stripe on the oriental hornet's abdomen may act as a solar cell. (Photo by MattiPaavola via Wikimedia Commons).

We’ve seen that autotrophs get their energy from sunlight or chemical reactions, while heterotrophs get their energy from eating other organisms. We’ve also seen that some protists, called mixotrophs, can do both.

We have not yet discussed reptiles, which are heterotrophs (as are all members of the Domain Animalia), but use the sun to regulate their internal temperature (they’re ectotherms).

According to a recent article, the yellow pigment on the oriental hornet’s belly can convert sunlight to electricity, and is believed to have some role in photosynthesis in some plants.

The researchers used the pigment to make their own solar cell, but it proved to be quite inefficient, only converting 0.335% of the incoming light to electricity. However, the microscopic ridges on the hornet, and the layering of the insect’s cuticle, suggest that the hornet itself is more efficient.

I’m not quite sure how the hornets would use the electricity if that’s what they’re doing, but they are more active in sunlight than in the dark, so some type of “solar harvesting” is probably going on.

Lego Mindstorms

I’ve been curious about the Lego Mindstorms robotic systems for a while now, and I had my first chance to try them at the St. Louis Science Center.

The kits come with a micro-controller, a few motors and some sensors. While there are quite a number of ways of assembling these to make robots, the ones at the science center were pre-built except that you could just plug in a bulldozer or sweeper attachment (and a head which was purely decorative). This limited the degrees of freedom to three, which made it easier to program something useful in the hour we had with the robots.

The programming is very basic. There are two sets of instructions, one to control the movement of the robot in general, and one to control its response when the sensor detected a change in the environment. The objective of the science center’s game was to clear off a set of objects from a white rectangle within five minutes.

You could tell the robot to move forward, back or rotate while it’s on the board and to activate its sweeper or shovel. So a full program could have just five elements; general: lower shovel –> move forward –> rotate; sensor: move backward –> rotate. With these strict limitations, the programming interface is also very simple; you plug in blocks with each instruction in the series for either the general movement or the sensor reaction. With all this simplification, I’m not sure just how much the students learned about programming from our short session.

The full kit from Lego offers more freedom to design robots and thus more flexibility with the programming interface so with a little thought it could be easily integrated into the curriculum. At about $300 each the system is a bit pricy, we’d probably need to get one kit for each small group of 3-4 kids. They would probably be worth it however if we used them more than just once.

I’ve been playing with the Basic Stamp micro-controller for a while, and while it offers almost infinite flexibility, making it more useful for practical applications, it does not provide the immediate gratification of the robots, and the ease of assembly to make it the better tool for introducing robotics to middle schoolers. I still, however, tend to favor practical applications, so perhaps I can persuade a student to do an advanced project to build an automatic window for the greenhouse.

The session at the Science Center was worthwhile. All of the students seemed to enjoy it. It provided a nice integration of the mechanics and electronics we’ve been learning about all year, and a glimpse of where technology is taking us in the future.

Pickwick Landing Hydroelectric Dam

[googleMap name=”Old Turbine” description=”Pickwick Landing Hydroelectric Dam” width=”490″ height=”490″ mapzoom=”14″ mousewheel=”false”]35.072711, -88.250578[/googleMap]

The hydroelectric dam at Pickwick Landing on the Tennessee River is an almost ideal place to observe electricity generation and transmission. It was a serendipitous discovery though. After our failure to arrange a tour of a dam in Arkansas on the last immersion, we did not even try with this one.

The dam is right next to Pickwick Landing State Park where we camp when visiting the Shiloh National Battlefield. We’d arrived early at the park on the day before our visit to Shiloh, and having seen the dam and its locks on Google Maps’ satellite image (click the satellite button on the map above), I thought it might be useful if we drove over.

Coming around the northern side of the dam we spotted, right next to a parking lot, an old turbine from the dam that had been set up for display. It is amazing how big these things are, but what was really neat is the fact that if you listened, you could hear the whine of the modern turbines coming from the generators deep inside the dam.

Standing over the old turbine was an enormous high-voltage wire tower, sparse metal frame and truncated arms like a benevolent grandparent leaning over a plump, but scared child. The line of towers are connected to the generation station in the dam by power substation just across the street from the old turbine. The substation’s large transformer drums were obvious even from across the road.

Crossing southward over the dam, there is a road that runs westward along the edge of the river that allows a good view of the downriver side of the locks. We were lucky enough to see a barge passing through, although with the traffic on the river the locks are probably always busy.

pickwick-locks — Barge exiting the lock.

When we got back to the park the students draw a diagrams of the dam. They don’t do nearly enough diagrams given the importance of drawing in connecting the body and the mind (something I plan on rectifying in the next cycle) so this was a good experience for them. It was also a reminder to always keep their writer’s notebooks with them because then they could have drawn their diagram while they were at the dam looking at the thing.

Build your own generator

If you don’t have a generator building kit, but do have a few magnets, some wire and a long nail, you can build your own generator using the instructions on William Beaty’s website, ‘Ultra-simple Electric Generator‘. The video gives excellent, detailed instructions, but there are also written instructions with a supplies list.

UPDATE: A small group of my students tried this and, despite the complaints, I thought it was a useful exercise. I’m looking forward to their presentation tomorrow.