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.