The Circuit That Won't Light
A group of students builds a simple circuit with a battery, a bulb, and two wires. Their bulb does not light. They check their materials: the battery is new and tested in another circuit where it lit a bulb, and the bulb is tested and works in another circuit. They notice that one wire is connected to the battery and the bulb, but the second wire is only touching the bulb's metal base and is not connected to the battery at all. A classmate says, "The bulb must be broken." Another says, "The battery is dead." The students want to find the real problem and fix it so the bulb lights.
1. Use the evidence to explain why the bulb is not lighting, and evaluate the two classmates' claims.
Read the worked answer
A bulb lights only when there is a complete, closed loop-a path that goes from one end of the battery, through the bulb, and back to the other end. In this circuit, the second wire touches only the bulb and does not connect to the battery, so the loop is broken. Electricity cannot flow in a complete circle, so the bulb does not light.
Evaluating the claims: 'The bulb is broken' is not supported because the bulb was tested and works in another circuit. 'The battery is dead' is not supported because the battery lit a bulb in another circuit. The evidence points to the open circuit (broken path), not to bad parts.
2. Describe how the students should fix the circuit, and explain how they would know the fix worked.
Read the worked answer
They should connect the loose end of the second wire to the other terminal of the battery, so the path is: battery terminal → wire → bulb → wire → other battery terminal. This closes the loop.
They would know it worked if the bulb lights. That is the test: a complete circuit makes the bulb glow. If it still does not light after closing the loop, then they could recheck connections or test parts again, but the evidence already shows the parts work, so the broken path is the most likely cause.