Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: Explain the cooling of an object in contact with an evaporating liquid
Learning Objective/s:
  • Describe the process of evaporation and the role of latent heat of vaporisation.
  • Explain how heat transfer from an object to an evaporating liquid causes cooling.
  • Analyse factors that affect the rate of evaporation and the magnitude of cooling.
  • Apply the energy‑balance equations to calculate the temperature change of an object during evaporation.
Materials Needed:
  • Projector and screen
  • Whiteboard and markers
  • Handout with diagram of heat flow
  • Thermometer (digital)
  • Small beaker of water
  • Rubbing alcohol (≈2 mL)
  • Worksheet for calculations
 Introduction:
Have you ever felt a sudden chill when you splash alcohol on your skin? You already know how specific heat capacity and latent heat describe energy changes. Today you will discover why an object cools when it touches an evaporating liquid and how to predict the temperature drop. By the end of the lesson you will be able to explain the cooling mechanism and perform a simple calculation of the temperature change.
Lesson Structure:
  1. Do‑now (5'): Quick quiz on specific heat capacity and latent heat of vaporisation.
  2. Mini‑lecture (10'): Explain evaporation, latent heat, and the energy‑balance equations using a diagram.
  3. Demonstration (10'): Apply rubbing alcohol to a surface with a thermometer and observe the temperature drop.
  4. Guided practice (12'): Pair work on worksheet calculations (Q = m Lv, ΔT formula).
  5. Concept‑mapping activity (8'): Groups list factors influencing evaporation rate and discuss their effect on cooling.
  6. Check for understanding (5'): Exit‑ticket – one‑sentence explanation of how evaporation cools an object.
Conclusion:
We recap that evaporation draws latent heat from both the liquid and any contacting object, causing a temperature drop that depends on factors such as surface area and airflow. Students hand in their exit tickets and receive a brief summary of key equations. For homework, complete the remaining worksheet problems and research another real‑world cooling application, such as sweating or evaporative cooling in buildings.