# Conductors and Insulators

Ages
1012141618+

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The electrical behavior of matter enables us to classify it into two categories:

• Conductors
• Insulators

All matter is made up of electric charges. A conductor contains large numbers of electric charges that are free to move around (in a metal, these are electrons).  A large current can pass through them. An insulator contains large numbers of electric charges, but they are not free to move around, and only  a small current can pass through them.

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• To introduce the  notions of conductors, insulators and electrical resistance.
• To approach the risk of electrocution.

The teacher plans a period of experimentation with the students divided into groups. He or she provides the following materials for each group in advance: a flat  battery, a bulb, a socket, conducting wires, connectors.

• Introduction to the subject

What is a battery? What is it used for?

How does one light the bulb with the battery? A current must flow through the bulb’s filament.

• Experimentation:

In the first set of instructions, the students use only the battery and the bulb: they light the bulb wiith the battery (direct contact).

In the second set of instructions, the students  use all of the materials provided: they light the bulb with the battery at a distance (they construct an electric circuit).

The students draw a diagram of their experiment.

• Explanation:

The teacher starts the animation “Electric Circuits”. He or she identifies, with the students, the various materials presented, then carries out a variety of virtual experiments by connecting and disconnecting each of the materials.  The students can, at their stations, build the circuits presented by the teacher.

Why does the lamp light, or not light? The teacher emphasizes the  idea of a closed circuit.

In what direction does the current flow? The teacher introduces the conventional principle for current flow, which is that current flows from the positive pole of the battery to its negative pole. What happens if we switch the battery poles?  For a bulb, the direction of the current isn’t important; it simply needs to flow.

How do we diagram an electric circuit?

The teacher compares the diagrams made by each group, notes the differences, and introduces the  need for a standardization (a convention). A given electric circuit must correspond to a unique diagram  that makes it identifiable by any scientist in the world.

The teacher presents the standard symbol for each component (battery, bulb, piece of metal, wire, connectors).

If a connector is disconnected, what happens to the switch?  The teacher points out that the switch is open whenever one of the connections is disconnected, regardless of which one it is.  The circuit can only be in one of two states: open or closed.   The switch reflects these two states.

• Synthesis:

Imagine the configurations that would enable us to light two bulbs with the same battery. Suggestion: use the animation “Series and Parallel Circuits”.

Can we replace the conducting wires  in the circuit with other objects (plastic ruler, paper clip, pencil lead, wood, a finger, a metal container…)?  Show the animation “Conductors and Insulators”.

Give examples of electric circuits around you.  What plays the role of the battery, the bulb, the switch… Draw a simplified standard diagram.

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