Conceptual Problems
Problem 1: The Foggy Mirror
Scenario: After taking a hot shower in a closed bathroom, the mirror becomes foggy. Why? Explanation:
- Hot shower produces warm water vapour.
- The mirror surface is relatively cooler than the vapour.
- When warm vapour touches the cool mirror, it undergoes condensation.
- Tiny water droplets form on the glass, creating the “fog.”
Problem 2: The Lid Droplets
Scenario: You cover a hot bowl of soup with a plate. When you lift the plate after a few minutes, water drips from it. Why? Explanation:
- Steam (water vapour) rises from the hot soup.
- It hits the cooler surface of the covering plate.
- The vapour condenses into water droplets on the underside of the plate.
Problem 3: Does Water Boil Faster with a Lid?
Scenario: If you want to boil water quickly, should you cover the pan? Answer: Yes. Explanation: Covering the pan traps the heat and the steam. The trapped heat increases the temperature faster. Additionally, it prevents heat loss through evaporation, allowing the water to reach its boiling point sooner.
Problem 4: Ironing Clothes
Scenario: Why do we sometimes spray water on clothes before ironing? Explanation: Spraying water dampens the fabric. When the hot iron touches the damp cloth, the water turns into steam rapidly. This steam penetrates the fabric fibers, loosening them and making it easier to remove wrinkles.
Problem 5: The “Sweating” Bottle
Scenario: A bottle of cold soda is taken out of the fridge. Can we weigh the water that appears on the outside to find out the humidity of the room? Analysis: Theoretically, yes. The amount of water that condenses depends on how much water vapour is in the air (humidity).
- On a humid day, a lot of water will collect quickly.
- On a dry day, less water will collect. This is a simple way to judge if the air is humid or dry!