Скачать или смотреть 🔥 Class 9 Science Chapter 1 | Important Q&A | Evaporation & Change of State | 90+ Marks Series 💯

📘 Class 9 Science Chapter 1 – Matter in Our Surroundings
🎯 Important Question Answers for Exams
📖 Based on NCERT | Easy Language | Full Explanation

💡 Perfect for quick revision and exam preparation!
👉 Watch till the end to understand all concepts clearly.
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✅ Question/Answers

Q1. Explain with example – “Change of state is a physical change.”

A change of state is a physical change because no new substance is formed, and the chemical composition of the substance remains the same.
👉 Example: When ice melts to form water or when water changes into steam, only the physical state changes (solid → liquid → gas), but it is still H₂O.


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Q2. Why does the temperature remain constant during the change of state?

During the change of state, the heat energy supplied is used to overcome the forces of attraction between the particles, not to increase the temperature.
👉 That’s why the temperature remains constant until the entire substance changes its state (e.g., during melting or boiling).


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Q3. What are the factors that affect evaporation?

The main factors affecting evaporation are:
1️⃣ Temperature – Higher temperature increases evaporation.
2️⃣ Surface area – Larger surface area increases evaporation.
3️⃣ Humidity – Lower humidity increases evaporation.
4️⃣ Wind speed – Higher wind speed increases evaporation.


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Q4. Why does evaporation cause cooling?

During evaporation, the particles of the liquid absorb energy from the surroundings to change into vapor. This absorption of heat from the surroundings causes a cooling effect.
👉 Example: When we sweat, evaporation of sweat cools our body.