Exploring Conductivity: Kid Circuits

Resource for Grades 3-8

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Media Type:
Video

Running Time: 3m 32s
Size: 10.6 MB

Source: ZOOM

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Exploring Conductivity: Lemon Battery II (Document)

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Background Essay

In the 21st century, billions of people rely on electrical energy in one form or another. Today, even in some of the most remote regions, electricity powers lights, radios, televisions, and many other devices that help people to be more productive, comfortable, and informed.

In some places, electricity is generated by hydroelectric dams or coal-fired power plants. In others it comes from self-contained units called "dry cells, " also known as batteries. Regardless of its source, the resulting electric current is the same -- it is the flow of electrons through a substance.

In order for electric current to flow, three conditions must be met. One is presence of a substance that allows electrons to move, or flow, easily through it. Such substances, called conductors, are made up of atoms that hold their electrons loosely, allowing them to flow freely to other nearby atoms.

The second requirement is the presence of a power source. Whatever its form, a source of electric current creates what is called a voltage difference, which pushes electrons through the circuit. The chemical reactions inside batteries produce voltage differences between one end of the cell and the other that result in electric current.

Lastly, electric current requires a closed circuit, a length of conducting material connected at each end to a power source that also passes through the "load," the object that makes use of the current. A closed circuit allows a direct, uninterrupted flow of electrons out from the power source and back again in a complete circular connection with no beginning or end.

As demonstrated in the video segment from ZOOM, kids can act as conductors of electric current, though compared with some other substances, they're not very good ones! How do we know this? The reading on the voltmeter, which measures the voltage difference, decreases as more and more cast members join hands. Now, if lengths of copper wire were connected to each other in place of the chain of kids, there would be little or no such decrease. This is because copper wire, like most metals, is a good conductor.

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Discussion Questions

What happens to the digital clock when the lemon is cut in half? Why?

What is a closed circuit?

What are conductors? Why does the cast member say that kids are conductors? Do you think human bodies are good conductors?

Why does the reading on the voltmeter drop as more cast members join hands?

How many more kids do you think could be added before the digital clock stops working?

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Transcript

(humming) (gasps) Ooh!

GARRETT: When Kaleigh and I did our lemon battery experiment, we discovered that electricity could pass through our bodies. What if you go like this?

GARRETT and KALEIGH: Ooh! Oh, yeah, it works! This is so cool!

GARRETT: The electrons are going through both of us and going into the clock! Oh, my gosh!

Well, Natalie e-mailed us this challenge to see how many people we can have the electrons go through and still have the clock on. Mike, do you want to come out and help me with this?

MIKE: Sure.

GARRETT: So, we know that if we disconnect any part of the circuit, it's not going to work. What if we cut it...

MIKE: Cut the lemon?

GARRETT: Yeah, cut the lemon.

MIKE: All right, all right, try that.

GARRETT: So, right when I cut it...

MIKE: It's going to disconnect as soon as the two lemons come apart. Here, try holding the two lemons. Does it...?

GARRETT: Oh, that's so cool! It's because the electrons go up through my arm, and then back down the other one to complete the circuit. Hey, wait a minute. Why don't you hold this one? If I hold this one, does it go off?

MIKE: It goes right off. So, when we hold hands, it turns back on. So, want to try more people?

GARRETT: That's so cool, yeah, sure. Aline, do you want to come out and help us?

ALINE: Sure.

MIKE: So the circuit's disconnected.

GARRETT: So the circuit's disconnected.

MIKE: You have to come between us.

GARRETT: And so if we hold hands, it might...

ALINE: Is it working?

GARRETT: It's still working!

ALINE: Oh, my gosh!

GARRETT: It's so cool! Estuardo, do you want to come on out and help us? Estuardo, come on over. So, this is four people. And it still works! Oh, that's so cool.

ESTUARDO: That's awesome!

CAROLINE: Hold on tight, guys.

SHING YING: Come on, Kortney!

ALINE: You guys, why don't we...

ALL: It works! (cheer)

CAROLINE: I didn't think it would work because I thought the resistance— like the flow of electrons— was going to...

SHING YING: Well, I guess because we're, like, all connected here, it goes through Mike and you and Estuardo.

ZOOMer: It's off. It's on. It's off.

GARRETT: You guys want to try it with the voltmeter now?

SHING YING: Sure.

GARRETT: Do you want to test it out first?

MIKE: Yeah, let's try it with the lemons first.

GARRETT: So let's see how much...

MIKE: Way up there.

GARRETT: So that's 16 millivolts. Now try...

MIKE: Let's try connecting hands.

GARRETT: So it's four or five.

MIKE: Four or five.

GARRETT: What do you think's going to happen if we add more people?

MIKE: I think there's going to be a definite decrease in voltage.

GARRETT: Yeah, me, too.

MIKE: The more people there are, the more resistance there's going to be from body to body, and I think this is definitely going to be decreased.

GARRETT: Caroline, do you want to come on up? So, you'll come in the middle. (gasps)

CAROLINE: Wow! It's the same!

GARRETT: In between three and four.

GARRETT: Kortney, you want to come on out?

MIKE: Hey, Kortney.

CAROLINE: We're testing the voltage of...

GARRETT: Almost four again. That's... it's a little bit less and that's got us on the three.

SHING YING: Come on, Aline!

ALINE: I don't know if it's going to work. Do you think it's going to work?

GARRETT: I don't think it's going to work.

ALL: (cheering)

ESTUARDO: Conductors are materials that allow electrons to move through them. The wires of the lemon battery are conductors. And we're conductors!

KORTNEY: The path that electrons flow through is called a circuit. When the circuit is connected, the electricity can flow. When the circuit is broken, the electrons can't flow.

SHING YING: So the next time you turn off a light, you can think about the fact that you're disconnecting a circuit. Uh, can somebody please reconnect the circuit? Thanks!