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QPage 11: Q6: HC Verma: Concepts of Physics - Volume 2 Heat and Temperature Page 11: Q6 Solution: Why do marine animals live deep inside a lake when the surface…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume water density increases monotonically as temperature drops, leading them to believe the coldest water sinks. You must recall the anomalous expansion of water, where density peaks at $4^\circ\text{C}$, causing colder surface water to rise and insulate the deeper, denser layers.

Why do marine animals live deep inside a lake when the surface of the lake freezes?

Step-by-Step Verified Solution

**Answer:** Marine animals live deep in a lake in winter because the densest water (at 4�C) sinks to the bottom while ice floats on top. **Step-by-Step Explanation:** Water has maximum density at 4�C. In winter, surface water cools below 4�C, becomes less dense, and rises. The denser 4�C water sinks. When the surface freezes, ice (density ~0.9 g/cm_) floats and acts as an insulating layer, preventing further heat loss. The bottom water remains at ~4�C, providing a habitable environment.

All Questions in this Chapter

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