One Bulb, One Cell, Thirty-Six Students
A Class 8 science teacher in a Belagavi school has 36 students, one 40-minute practical period a week, and a kit containing two dry cells, a cell holder, six bulbs, six lengths of wire and one bulb known to be working. The chapter is electric current. In a pre-test, 27 of 36 students agreed that the current gets used up as it goes round, so the bulb near the battery is brighter, and 24 said a bulb will not glow if the wire touches only one terminal. The teacher's plan is a five-minute demonstration with one cell and one bulb, followed by dictating the definition of a circuit, because the practical period is short and two chapters remain. Last year the same demonstration was given; in the annual examination 19 students reproduced the circuit diagram correctly, but the same misconceptions reappeared in the application question.
1. Why did last year's demonstration fail to change the misconception, even though students could draw the diagram?
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A demonstration shows that the bulb glows; it does not show why, and it never touches the belief that current is used up. Conceptual change needs four conditions: the learner must be dissatisfied with the existing idea, and the new idea must be intelligible, plausible and fruitful. A demonstration creates none of these unless the student has first committed to a prediction and then seen it fail.
Passive observation is also easy to reconcile with the misconception. The claim that the bulb near the battery is brighter survives a single-bulb demonstration because nothing in that demonstration contradicts it. That is exactly why 19 students could draw a correct circuit and keep the wrong model: the diagram is a label, the model is a belief. The application question failed because it asked for the model, not the label. Time saved by demonstrating is therefore lost twice, once in the lesson and again in the examination.
2. Design a predict-observe-explain sequence that works with this kit for 36 students in 40 minutes.
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Do not run six groups at once; run a predict-first sequence with the whole class watching one bench.
Eight minutes: in six groups of six, students write predictions, with reasons, for three setups: wire on one terminal only; wire on both terminals; two bulbs in one loop. No apparatus is visible yet.
Fifteen minutes: one group demonstrates each setup at the front while every group records what happens. Groups whose prediction was wrong mark their sheet; that mark is the conflict, and it is why the prediction came first.
Ten minutes: discussion of the two-bulb case. Are both equally bright? Take a vote, then check.
Seven minutes: each student writes the explanation in their own words; two groups read theirs out.
The single known-good bulb and two cells are enough: the point is the two-terminal test and the series comparison, not the number of kits. State explicitly that the known-good bulb is the control, so a non-glowing bulb is evidence about the circuit, not about the bulb.
3. Write three assessment items that would distinguish a held misconception from a memorised statement.
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- Novel arrangement: a cell, two bulbs in one loop, and an extra wire connecting the two terminals of the first bulb. Predict the brightness of each bulb and explain. A student holding the used-up model predicts the second bulb is dimmer; a correct model predicts the shorted bulb goes out.
- Fault diagnosis: a bulb does not glow. Give two different reasons and the test that would tell them apart. This requires the circuit model and a design, not recall.
- Argument: a student says the current is smaller after the bulb. What would you show them to settle it? This requires the student to plan evidence.
Mark the reasoning, not the keyword. Keep the original pre-test items as a post-test and compare how many students now reject the used-up model. That shift, not the diagram score, is the learning gain, and it is the number to report when the two pending chapters are raised as a reason to cut the practical period.