Lesson Plan

• Describe how good and bad infrared emitters differ in emissivity.
• Explain Kirchhoff’s law relating emissivity and absorptivity for IR radiation.
• Conduct and record data from at least two classroom experiments that compare IR emission of different materials.
• Analyse temperature or radiometer data to determine relative emissivity of test surfaces.
• Evaluate safety considerations when handling IR sources and heated equipment.

• Cardboard boxes or sealed containers
• Sensitive thermometers or thermistor probes
• Hot plate with temperature control
• Crookes radiometer with interchangeable vane covers
• Infrared (IR) thermometer (non‑contact)
• Test material samples (black matte sheet, polished aluminium, white glossy sheet)
• Heat‑resistant gloves and safety goggles
• Data recording sheets or worksheet

Begin with a quick demonstration: hold a black matte card and a shiny aluminium foil over a warm hand and ask students which feels hotter. Recall that all objects above absolute zero emit infrared radiation and that emissivity governs how efficiently they do so. Today’s lesson will enable students to design and carry out simple experiments to identify good versus bad IR emitters and to interpret the results against the success criteria.

1. Do‑Now (5’) – Students answer a short question on why dark surfaces feel warmer than shiny ones, recording predictions.
2. Mini‑lecture (10’) – Review infrared radiation, emissivity, and Kirchhoff’s law with illustrative diagrams.
3. Group Activity – Thermometer‑in‑a‑Box experiment (15’) – Students set up the box with black and aluminium covers, record temperature rise after 5 minutes.
4. Group Activity – Radiometer experiment (10’) – Teams attach different material covers to the radiometer, observe rotation speed, and note observations.
5. Group Activity – IR thermometer test (10’) – Measure IR temperature of heated samples using the non‑contact thermometer and compare readings.
6. Data analysis and discussion (10’) – Teams calculate ΔT, compare results across methods, and relate findings to emissivity concepts.
7. Safety recap and clean‑up (5’) – Review key safety points and ensure equipment is turned off and stored safely.

Summarise that materials with higher absorptivity produce larger temperature rises, faster radiometer rotation, and higher IR‑thermometer readings, confirming they are good emitters. For the exit ticket, each student writes one practical implication of knowing a material’s IR emissivity. As homework, students research an everyday application (e.g., thermal clothing or building insulation) where emissivity is critical and prepare a brief paragraph.