Conductors and Insulators

Preamble
The terms "conductors" and "insulators" are not introduced until the end of the session. This is in accordance with the literature (and my personal experience) that supports giving students a concept before giving it a label makes it easier for the students to remember both the concept and the label.

The class should be put in groups of three or four students.

Equipment
Each group is given:
 * 1 flashlight bulb
 * 6 wires with crocodile clips
 * 1 D battery in a holder
 * a selection of about six objects. For example, a rubber band, a straw, a Popsicle stick, a paper clip, a pencil sharpened on both ends, a piece of string.

Challenge
Using the equipment you have been given, find out what kind of substances allow electricity to flow through them.

Before beginning you need to decide:
 * 1) How you will determine if a substance allows electricity through it
 * 2) How you will record your results

Please try to test about 15 substances.

Please write down and have ready to hand in:
 * 1) the names of your groups, the date, a diagram of the circuit you used, your results
 * 2) what type of substances allow electricity to flow through them. Can you give a category for the substances that allow electricity to flow?

Teacher: Circulate around the groups and engage them in discussion. In my experience, the students know exactly how to test that electricity flows through a substance, but tend to write their results in paragraph format. I try to encourage them to use tables.

I prefer to take the papers in from the groups at this point and look at them before coming to a whole class discussion.

Talk with the class about the idea that metals are conductors and other substances are not. Pencil "lead" is an exception and usually the only exception they find. Every class I have done this with have stated that metal "works" and other substances do not "work". This is a fun discussion about what "work" means and I have approached it differently every time according to exactly how the students have brought it up. Introduce the terms "conductors" and "insulators". Discuss the situations for which we need a conductor and those for which we need an insulator. I find this generally turns into a safety talk on electricity. The students bring up situations that they have experienced or they have been taught (such as taking toast out the toaster using a knife, or pulling a plug out by the cord rather than the plug itself). In this way, I manage to teach safety without the students really being aware of what I am doing. For my students this is better than a safety talk which they roll their eyes at.

Extension

 * Research into semi-conductors and super-conductors may interest some students, or be a useful assignment for students who need more of a challenge.
 * Ask students to find out if there are any plastics that conduct electricity.

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