This instructable is of a unit I do with my honors physics students to help them construct for themselves an understanding of how every part of an electric circuit works, and why it does what it does. I have broken down the unit into a series of objectives with an explanation of what students do to achieve that objective. The inspiration for this series of investigation is the CASTLE curriculum which was written by a committee of physics teachers in the 1980's.

An inexpensive source of mini incandescent bulbs is older strings of holiday lights. As people replace their holiday lights with lower energy LED lights, ask for their old light strings. All you have to do is cut apart the lights and strip the ends of the wires. These holiday bulbs are very sturdy and difficult to blow out even if students connect them to more batteries then they should during their investigations.

The unit is broken into a series of research questions:

What is the minimum needed to light an incandescent bulb?
Is there anything happening in the wires of a circuit when a light bulb is lit?
Which materials are insulators and which are conductors?
How does an incandescent bulb work?
How do resistors effect the charge flow through a circuit?
How do the resistance of your two different types of bulb and connecting wire compare?
How is the total resistance of your circuit effected by adding a bulb in parallel?
What does a capacitor do in a circuit?
What does a generator do in a circuit?
Does a battery have internal resistance?
What causes electric potential difference changes in the wires?
How does electric potential difference (volts) divide among components in a series circuit?
How does electric potential difference (volts) divide among components in a parallel circuit?
How does current vary around a series circuit?
How does current vary among the branches of a parallel circuit?
Do flow paths influence the electric potential difference between battery terminals?
How does voltage vary as a capacitor charges?
How do you use a voltmeter and an ammeter to make measurements in a circuit?

At the beginning the investigation questions are followed by more detailed instructions as to how to answer that question, but as the investigations continue less and less guidance is given for the students as they build their mental model of how electric circuits operate. I give quizzes after each five questions to make sure that students are building appropriate knowledge and gathering sufficient evidence for their model to correctly interpret what is happening in the circuits.

Step 1: What is the minimum needed to light an incandescent bulb?

Learning Objective:
  • Determine what the minimum requirements are to light an incandescent bulb.

Materials: mini incandescent bulb, bulb socket, battery case, D cell batteries, connecting wires

Design a circuit that contains the minimum materials needed to light an incandescent bulb. (You do not need to use all of the investigation 1 materials for this circuit.)

Lab questions
1.  Build a circuit with three D-cell batteries and two mini incandescent bulbs in a closed loop. Break the loop by disconnecting a wire from one end of the battery holder and then reconnect it.  Do both bulbs appear to light at exactly the same time?  Do you believe that both bulbs actually light at the same time?
2.  Reconnect the wire to the battery, and then disconnect a different wire somewhere else in the loop.  Try this in several places.  Is there any place where you can break the loop and one or both of the bulbs will still stay lit?
3.  Unhook one of the wires and bring it as close as you can to where it was connected  without actually making contact.  Do this slowly and carefully, watching the space between the wire and the contact point. Do the bulbs light? Do you think actual contact is needed for the bulbs to light continuously?
You are too awesome citizen!!!
This is an excellent lesson/unit write-up. All that's missing for this to be perfect are varied pictures. Awesome work, though. I'd double-feature it if that was an option.

About This Instructable


112 favorites


Bio: I'm a physics and chemistry teacher at a public school in Maryland and active in my local science teacher's association. I love building ... More »
More by CitizenScientist: Modeling the Chemistry around You Investigating Energy Transfer in Ocean Waves Work, Power, and the Conservation of Energy through Roller Coasters
Add instructable to: