Discovery question

How does electricity move?
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IMAGE: ELECTRONS MOVING THROUGH A METAL LATTICE – USE THIS ALSO IN PAUL'S STORY

Build a model of how electrical charges travel in a circuit and move energy from one place to another.

H3. Engage
In an electric circuit, such as a battery and a light bulb, the charges are free to move around the circuit. If they are pushed through the light bulb, it heats up and glows. The battery provides the "push".

You can model this process with a circle of students. Form a circle with everyone linking arms, including the teacher. Pretend that the teacher is the battery and a student across the circle is the light bulb.

Let the teacher give a little pull. This is like what a battery does. Right away, every other person feels the pull. The pull goes right around the circle.

Let the person who is the light bulb try to not move. They will feel pushed on one side and pulled on the other. The effort that they must make to try not to move is like the energy the light gets from the battery that makes it heat up.

Now build a similar model of a circuit using string and straws.

Materials

• piece of cardboard 25 x 50 cm (10 x 20 in)
• bendable straws
• string, pushpin
• tape
• marker

Explore

Make a necklace of four bendable straws on a piece of string.

Tie the string into a loop, leaving about 20 cm of string that is not inside the straws.

Tape the necklace to a piece of cardboard in a rough rectangle. Leave the string a little loose. Leave two areas where the string is not inside the straws.

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Put a dot on the the string about every centimeter. These represent electric charges that can move inside the wire.

Pull the string to make it go around the loop. This is what a battery does. It forces the electric charges along the wire. Draw in a picture of the battery on a piece of paper and stick it to the cardboard.

Have one person press down lightly on the string and another person pull the string in another place to make it go around. What happens?
ANSWER BOX

Draw a picture of a light bulb and stick in on the cardboard where the person is pressing on the string.

Explain

This model is like an electric circuit in some ways. Here is a picture of an electric circuit showing electrons moving along the wires. Of course real electrons are very, very, very small. We can't see them.
ANIMATE THIS?
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Elaborate

What if you cut the string? Could you move charges around the loop?
ANSWER BOX

Cutting the string is like opening a switch. Draw in a picture of a switch somewhere along the wire.

Evaluate

This model is like an electric circuit in some ways. It is meant to be an analogy. Here is a comparison between your string circuit and a real electric circuit.

TABLE String circuit Electric circuit Must make a loop for the string to move    Must make a loop for the electricity to flow Dots on the string    Electric charges in the wire Straw    Wire String in a straw    Electric charges in a wire Pull the string    Battery pushes and pulls charges Pinch the string, making resistance    Resist the flow of electric charges (electric resistance Energy to pull the string if it is pinched    Energy to make the electric charges flow when there's resistance, as in a light bulb or a motor When you move the string in one place, all the dots move at once    When you hook up the circuit, the charges in the wire all move at once.

Here are some ways this analogy is not correct!

TABLE String circuit Electric circuit String moves through the straw    The wire does NOT move through the straw – just the electric charges move Dots move slowly    Charges move very fast You can see the dots    Electric charges are too small to see