Directing Electricity

Imagine this.  You are standing by Volta’s long table, looking at the little towers of metal discs.  You ask, “So electricity is flowing out of one of these all the time?”

Volta nods.  “As long as the materials inside continue doing their work, yes.”

“That seems much more useful than Franklin’s jars,” you say.

“It is,” Volta agrees, “but it is not enough.”

“Not enough?  What do you mean?”

“We were talking about a water wheel before.  But how do we power that wheel?  That is the question.  The Leyden jar isn’t helpful, because it is like dumping a bucket of water on the water wheel—one quick zap and then it’s over.  These towers are more promising, because they provide a continuous flow, like a river, and a river is exactly what we need to power a water wheel.”

“Okay,” you nod, “I think I understand that.”

“But suppose you are trying to power a water wheel with a river, and then the river floods.  It overflows its banks, flows over farms, fields, roads, houses.”

You picture it.  “That would be a problem.”

“Right,” Volta says.  “The power of a river is not simply that it flows.  It also matters where it flows.  So, to make electricity useful, we must control where it flows.”

Volta points to a water pitcher on the table and invites you to pick it up.  Then he asks, “If you pour the pitcher out over the table, will you have much control over where the water ends up?”

“Not much,” Dustin replies.  “The water will splash around everywhere.”

Then Volta picks up a long glass tube from the table.

“What if you poured water in here?”

“The water would flow through the tube,” Dustin says.

“And where would the water go?”

“Wherever the tube goes.”

Volta hands the tube to Dustin.  “So with this tube, you could control where the water ends up?”

“It seems so.”

“Show me,” Volta says.

Dustin then places one end of the tube in a bowl, and you pour water through the other end.  As predicted, the water flows from one end of the tube and into the bowl.

Volta smiles.  “Now we are getting somewhere.  Do you see?”

“No,” Dustin says.

“We control the flow of water with pipes, right?” Volta says.  “We need to control the flow of electricity in the same way.  Do you see now?”

“No.”

Volta looks at Dustin for a moment and blinks.  “Think about Franklin’s Leyden jars,” he says.

“Okay.”

“What did those do?” Volta asks.

“Those stored electricity,” Dustin says.

“Right,” Volta says.  “And think about the little towers over there.  What did they do?”

“Those made electricity flow.”

“Right.  So what do we need to do now?”

“I don’t know,” Dustin says.

“Well, what did you just do with the tube?” Volta says.

“We filled a bowl with water,” Dustin says.

“Right, but why?” Volta says, growing a little impatient.  “Do you not see the connection?”

Feeling a little sorry for Volta, you step in with an answer.  “We need to control where electricity flows,” you say, “just like the tube controlled the flow of water.”

“Exactly,” Volta says, with evident relief showing on his face.

“Okay,” Dustin says, “but we can’t just pour pitchers of electricity down a tube.  That’s dumb.”

You think for a moment about the problem, and then ask, “Are there pipes for electricity?”

Volta walks to another part of the table and picks up a wire.  “Yes there are,” he says as he hands the wire to you.  “Wires are the pipes.”

Dustin snatches the wire from your hand and inspects it.  “This won’t work,” he declares.

“Why not?” Volta asks, looking quite surprised.

“It’s not at all like a pipe,” Dustin explains.  “There are no hollow parts in this wire.  Nothing can flow through it.”

“I see,” Volta says.  “Water needs hollow spaces to flow.  But electricity doesn’t.  It flows through certain kinds of materials.  This wire is made of copper, and electricity can flow quite freely through copper.”

“Are there other kinds of materials that electricity can flow through?” you ask.

“Yes, there are many kinds,” Volta says.  “Those kinds of materials are called ‘conductors.’”

“Not all materials, though?” you ask.

“Not all materials.  Think about our pipe example.  A pipe needs a hollow space for water to flow.  But a pipe needs more than a hollow space.”

“What do you mean?”

“Well, if a pipe were only hollow space, then would it even be a pipe?”

“I’m confused,” Dustin says.  “This is crazy.  What is a pipe without walls?  It would literally be nothing.”

“My point is that the walls around the hollow core are necessary to keep the water inside,” Volta says.  “A pipe needs hollow space for the water to flow through, but it also needs material that keeps the water flowing in the right direction.  That makes sense, right?”

“It does,” you assure him.

“Fine,” Dustin says, “but we are supposed to be talking about wires, not pipes without walls that don’t exist.”

“Pipes need walls to keep the water flowing in the right direction,” Volta repeats, “and it is the same with wires.  The core of the wire needs to be a conductor material—like the copper here—which is the space for the electricity to flow.  But the wire also needs ‘walls’—that is, material that keeps the electricity inside the wire, flowing in the right direction, rather than splurting out everywhere.”

“How do you put walls around a wire?” you ask.

“Some materials are conductors, like we said,” Volta explains, “but other materials aren’t.  We call them ‘insulators.’  Those are materials that don’t let electricity flow.  They stop electricity from flowing.  So if you put an insulator material around a conductor material, then you have a pipe for electricity.  The electricity will flow through the conductor part, and won’t break through the insulator part.”

You nod.  “I think I understand that.  That’s pretty clever.”

“It’s only clever if you know which is which,” Dustin says.  “Otherwise you can’t make these pipes.  And I can’t tell which is which.  Can you?”

Volta folds his arms and looks down at the table in front of you.  There you see a collection of objects spread across the table.  There’s metal, wood, glass, rubber, cloth, paper.  

“Well, funny you should ask,” Volta says.  “I could really use your help figuring that out.”

“My help?!” Dustin asks.  “On what?”

“Well, I’d prefer that both of you work together on this,” Volta clarifies.  “I need help finding materials that are good pipes and finding materials that are good walls.”

“But how am I supposed to know that?” Dustin asks.

“There is only one reliable way to learn,” Volta responds.

“What’s that?” Dustin asks.

“Test them,” Volta says, gesturing toward the materials waiting on the table.  “Discover which things behave like pipes and which things behave like walls.”

“Hm,” Dustin grunts.  “It would be easier if you just told us.”