🌬️ 1.5 – Evaporation

🌬️ 1.5 – Evaporation

(From Chapter: Matter in Our Surroundings – Class 9 CBSE)

📘 What is Evaporation?

Evaporation is the process by which liquid changes into vapour at any temperature below its boiling point.

✅ It is a surface phenomenon — it occurs only from the surface of the liquid.

🔍 Why Does Evaporation Occur?

  • In a liquid, some surface particles have more kinetic energy than others.

  • These high-energy particles overcome the force of attraction and escape into the air as vapour.

  • This can happen even at room temperature.

🧠 Important Points:

  • Evaporation is different from boiling:

    • Boiling happens at boiling point

    • Evaporation happens at any temperature

🧪 Real-Life Examples of Evaporation:

  • Wet clothes dry in the sun

  • Water in a bowl disappears when left out

  • Sweat evaporates, keeping our body cool

  • Perfume disappears after a while

  • Alcohol/acetone feels cold on skin

🔁 Factors Affecting the Rate of Evaporation

Factor Effect & Why
Temperature ↑ Temperature → ↑ Kinetic energy → ↑ Evaporation
Surface Area ↑ Area → More particles can escape → ↑ Evaporation
Wind Speed ↑ Wind → Carries away vapour → ↑ Evaporation
Humidity ↑ Humidity → ↓ Evaporation (air already full of vapour)

📘 Cooling Effect of Evaporation

When a liquid evaporates, it takes away heat from the surface — this causes cooling.

✅ Examples:

  • Sweating cools the body

  • Earthen pots (matkas) keep water cool

  • Rubbing alcohol or acetone feels cold

📎 Key Differences: Boiling vs Evaporation

Boiling Evaporation
Occurs at boiling point Occurs at any temperature
Fast process Slow process
Happens throughout the liquid Only from the surface
Needs external heat Can happen naturally

📘 CBSE Connection:

Evaporation helps explain why clothes dry, why animals sweat, and how nature balances water in the environment — it's a part of the water cycle!

💬 Ask Your Students:

  1. Why do wet clothes dry faster on a sunny and windy day?

  2. Why do we feel cold after applying perfume or alcohol?

  3. Why does water in a clay pot remain cool?

🎤 Closing Line for Class:

“Evaporation is invisible, but powerful — it cools your body, dries your clothes, and keeps nature in balance. Science in action, one drop at a time!”

Would you like a worksheet, chart of differences between boiling and evaporation, or a quiz on this topic?

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