Explain how condensation on a cold glass leads to water droplets forming on its surface. Why does this happen even though the glass feels cold?
Answer
When warm moist air touches a cold glass, the air cools down to its dew point. The water vapour condenses into liquid water droplets on the surface of the glass. The glass is cold enough to lower the temperature of the air above it below the dew point, causing the condensation.
Step-by-step solution
- State that the glass is colder than the surrounding air.
- Explain that the warm moist air rises above the glass and cools.
- Mention the concept of dew point: the temperature at which air becomes saturated.
- Describe that when the air temperature falls below the dew point, water vapour condenses into droplets on the cold glass.
- Conclude that the glass feels cold because it transfers heat to the air, cooling it enough for condensation.
Common mistake: Missing the role of the dew point or confusing condensation with evaporation.
Concept tested: Condensation and dew point
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