Heat and Energy
ICSE · Class 9 · Physics
Quick revision notes for Heat and Energy — ICSE Class 9 Physics. Key concepts, formulas, and definitions for last-minute revision.
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1. Heat and Temperature
- Heat is a form of energy due to the internal energy of molecules in a body.
- Heat flows from a hot body to a cold body when the two bodies are in contact.
- A hot body has more internal energy than an identical cold body.
2. Thermal Expansion and Anomalous Expansion of Water
- Almost all substances expand on heating and contract on cooling.
- The expansion of a substance on heating is called thermal expansion.
- Solids expand in length, area, and volume on heating.
3. Hope's Experiment
- In 1805, T.C. Hope devised Hope's apparatus to demonstrate anomalous expansion of water.
- Hope's apparatus is a tall metallic cylinder with two side openings.
- The upper opening P has thermometer T1 near the top.
4. Consequences of Anomalous Expansion of Water
- In winter, water at the surface of a pond cools and sinks until the whole water body reaches 4°C.
- Below 4°C, water expands and becomes less dense, so it stays on top.
- The top layer can freeze into ice while deeper water remains liquid.
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