| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: explain that the resistance of a filament lamp increases as current increases because its temperature increases |
Learning Objective/s:
- Describe how temperature affects the resistivity of a metal filament.
- Explain why a filament lamp’s resistance rises as the current through it increases.
- Apply the temperature‑coefficient formula \(R = R_0[1+\alpha(T-T_0)]\) to predict resistance changes.
- Analyse a V‑I characteristic of a filament lamp and identify its non‑ohmic behaviour.
- Solve simple circuit problems that include a filament lamp using iterative reasoning.
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Materials Needed:
- Projector or interactive whiteboard
- Variable power supply with a filament lamp demo kit
- Multimeter (voltage and resistance)
- Worksheet containing calculations and graphing tasks
- Graph paper or digital plotting software
- Scientific calculators
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Introduction:
Begin with a quick demonstration of a lamp getting brighter as the voltage is increased, asking students what they notice about the current and brightness. Recall Ohm’s law and the concept of resistivity from previous lessons. State that by the end of the lesson they will be able to explain the physical reason behind the lamp’s changing resistance and predict its behaviour.
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Lesson Structure:
- Do‑now (5 min): Short quiz on Ohm’s law and resistivity; teacher checks answers.
- Mini‑lecture (10 min): Introduce temperature coefficient α and derive \(R = R_0[1+\alpha(T-T_0)]\); show slide with tungsten data.
- Live demonstration (10 min): Vary voltage on a filament lamp, record current and voltage with a multimeter; discuss power \(P = I^2R\) and heating.
- Guided calculation (12 min): In pairs, use the provided temperature‑resistivity table to calculate resistance at 1500 °C and 2500 °C; complete worksheet.
- V‑I curve analysis (8 min): Plot the measured points, identify the non‑linear trend, and relate it to temperature‑dependent resistance.
- Exit ticket (5 min): Write one concise sentence explaining why the lamp’s resistance increases with current.
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Conclusion:
Summarise that the filament’s temperature rises with increased power, causing its resistivity—and therefore resistance—to increase, which makes the lamp a non‑ohmic component. Collect exit tickets and remind students to complete a homework task: calculate the expected resistance of a tungsten filament at a given temperature using the α value. This reinforces the quantitative link between temperature and resistance.
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