Heat — Class 6 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 6 Science, Term 2 — Chapter 1. Heat, temperature and how heat travels.
1. About this chapter
This chapter covers heat and its sources, temperature, thermal expansion, thermal equilibrium, and the methods of heat transfer.
2. Heat and temperature
- Heat is a form of energy; its unit is the joule (J). When an object is heated, its molecules move faster.
- Temperature measures the average kinetic energy of the molecules of a body.
- Sources of heat: the Sun, the burning of fuels (coal, wood, charcoal, gasoline), and electric current flowing through a conductor.
3. Thermal expansion and equilibrium
- Thermal expansion is the expansion (increase in size) of a substance on heating. Solids, liquids and gases all expand on heating.
- Thermal equilibrium is reached when two objects in contact no longer change each other's temperature — e.g. 1 L of water at 30 °C mixed with 1 L at 50 °C reaches about 40 °C.
4. How heat travels
| Method | Where it happens |
|---|---|
| Conduction | in solids — heat flows from the hotter to the colder region |
| Convection | in liquids and gases (the warm part rises) |
| Radiation | through empty space (no medium needed) — how the Sun's heat reaches us |
5. Worked examples
Example 1. What is the unit of heat? The joule (J).
Example 2. In which method of heat transfer is no medium needed? Radiation.
Example 3. 1 L of water at 30 °C is mixed with 1 L at 50 °C. Find the final temperature. About 40 °C (the average).
6. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- When an object is heated, its molecules — (a) move faster / (b) stop. Ans: (a) move faster.
- The unit of heat is the — (a) joule / (b) metre. Ans: (a) joule.
- 1 L of water at 30 °C mixed with 1 L at 50 °C reaches about — (a) 40 °C / (b) 80 °C. Ans: (a) 40 °C.
- Convection of heat takes place in — (a) solids only / (b) liquids and gases. Ans: (b) liquids and gases.
II. Fill in the blanks 5. Temperature measures the average kinetic energy of molecules. 6. The expansion of a substance on heating is called thermal expansion. 7. In conduction, heat flows from the hotter to the colder region.
III. Answer briefly 8. Name three sources of heat. — The Sun, the burning of fuels, and electric current. 9. What is thermal equilibrium? — When two objects in contact no longer change each other's temperature.
7. Common mistakes
- Mistake: Saying heat and temperature are the same. Fix: Heat is energy (joule); temperature measures the average kinetic energy of molecules.
- Mistake: Thinking convection happens in solids. Fix: Convection occurs in liquids and gases; conduction in solids.
- Mistake: Saying radiation needs a medium. Fix: Radiation needs no medium (the Sun's heat reaches us through empty space).
8. Quick revision
- Term 2 · Ch 1 · heat.
- Heat = energy (joule); heating makes molecules move faster; temperature = average kinetic energy.
- Sources: Sun, burning fuels, electric current; thermal expansion = expansion on heating.
- Heat travels by conduction (solids, hot→cold), convection (liquids/gases), radiation (no medium).
