Circuits

Frances Uku
and
Emily Wood

1. What is electricity? Can you see it? Smell it? How do you know it is there?
2. Where do you get electricity at home? (likely response: from the wall, or from PG&E)
3. Where does it go? (likely response: into your blow dryer, coffee maker or microwave)
4. Imagine a bucket, and you use a hose to pour water into it, after a while what would happen? (the bucket overflows)
5. So why doesn’t your blow dryer or microwave over-flow?
6. The electricity needs some place to go, so we send it back into the wall, like a loop. Have you ever heard the term “circuit?” Where have you heard it? What does it mean to you?

• One D battery
• Several long strips of aluminum foil
• Two large paper clips (plain metal, no coatings)
• Two small light bulbs (less than 8 Watts, available at Radioshack)
• Two large rubber bands
• Optional: several 8” lengths of magnetic wire, left over from the electric motor lesson (you will also need sandpaper or emory boards to remove the insulation)

Experimental Procedure:

Challenge the students to light the light bulb. Let them figure out how and what is required (a completed circuit, although it is not necessary to use the term “circuit” at this point). To give hints, ask them where the electricity is going in their particular setup, is there a place for the electricity to go? Encourage the students to write down there setups and observations.

1. Determine what type of “wire” is most effective: magnetic wire, aluminium foil, or unfolded paper clip.
2. Determine how to light two light bulbs at the same time. Is there only one setup possible? (parallel versus series). Can you light more than two light bulbs?
3. Which makes the bulbs light up brighter, parallel or series? Why do you think this is?
4. Determine the effect of number of batteries on the circuit. Why do the bulbs get lighter?

1. As all good scientists do, you probably made a few observations, what did you notice? (list observations, correct or incorrect on the board)
2. What was necessary to make the light bulb light?
3. What you made is called an electric circuit, one of the key tools for scientists today.
4. Did anyone get more than one lightbulb to light? Can you draw your setup on the board?
5. This is a larger form of the circuit. In fact, most circuits are even more complex. All are based on the idea of allowing electricity to flow continuously, so the bucket does not over-flow.
6. Any questions?

Depending on the level of the class, and the students’ exposure to physics, more depth may be desirable into circuit theory. Consider explaining how lightbulbs work: resistance creating heat and causing filament to glow. Another suggestion is to explain how series and parallel circuits differ, although this requires some background in resistance, current, and voltage which may be more appropriate for a second lesson.