Скачать или смотреть Water Reboiling Experiment Explained | Which Operation Fails? ( CSCA physics Final Exam)

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Water reboiling is one of the most classic and exam-favorite Physics experiments 🔥
This question almost always appears in Class 8 final exams, especially in the chapter related to heat, pressure, and boiling point.

In this video, we carefully analyze a reboiling experiment MCQ and explain why only one option fails to make water reboil.

📘 Question Overview

During a water boiling experiment:

Water is first heated until it boils

The heat source is removed

The flask is sealed tightly

After that, different operations are performed.
The question asks:

👉 Which operation cannot make the water boil again?

💡 Key Physics Concept

To understand reboiling, we must remember:

✅ Boiling point depends on air pressure

Higher pressure → higher boiling point

Lower pressure → lower boiling point

If the boiling point suddenly drops below the current water temperature, the water will start boiling again.

🔍 Why Does Water Reboil?

After boiling, the flask contains:

Hot air

Hot water vapor

When certain operations are done:

Water vapor cools and condenses

Gas volume reduces sharply

Air pressure inside the flask suddenly drops

This sudden pressure drop lowers the boiling point of water.
Since the water temperature is still high, it becomes superheated and starts boiling violently again.
This is called reboiling or explosive boiling.

🧪 Option-by-Option Analysis
✅ Option A: Pouring cold water on the inverted flask

Cold water cools the gas and water vapor at the top

Vapor condenses rapidly

Air pressure drops

Boiling point decreases

✔ Water reboils
✔ Option A works

❌ Option B: Pouring cold water at the bottom of the flask

Cold water cools the liquid water directly

Water temperature decreases

Boiling becomes harder

❌ No pressure reduction
❌ No reboiling

🚫 Option B does NOT work

✅ Option C: Placing ice on the inverted flask

Same principle as cold water

Gas and vapor cool and condense

Pressure drops

✔ Water reboils
✔ Option C works

✅ Option D: Using a syringe to remove air

Gas is directly extracted

Air pressure decreases

Boiling point drops

✔ Water reboils
✔ Option D works

✅ Final Answer

👉 Correct Answer: B

🎯 Why This Question Is Important

✔ Very common experimental MCQ
✔ Tests understanding of pressure vs boiling point
✔ Easy to confuse if the concept is unclear
✔ High chance in board & final exams

📝 Exam Tips

✅ Reboiling happens due to pressure drop, not heating
✅ Cooling the gas, not the water, causes reboiling
✅ Vapor condensation = pressure reduction
✅ Remember: Lower pressure → lower boiling point

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