Heat — Class 9 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 9 Science, Physics — Chapter 7. Heat is a form of energy that flows due to temperature differences. Understanding thermal expansion, heat transfer, specific heat capacity, and latent heat explains climatic patterns, thermometers, and engine cooling.

1. About this chapter

This chapter covers thermal energy, temperature scales, modes of heat transfer, specific heat capacity, and latent heat.

2. Heat and Temperature

• Heat: Flow of thermal energy. Unit: joule (J).
• Temperature: Measure of average kinetic energy of molecules. Unit: kelvin (K) or celsius (°C).
• Conversion: $\frac{C}{5}=\frac{F-32}{9}=\frac{K-273}{5}$.

3. Modes of Heat Transfer

• Conduction: Heat transfer in solids without actual particle movement.
• Convection: Heat transfer in fluids due to movement of density currents.
• Radiation: Heat transfer without a medium (via electromagnetic waves).

4. Specific and Latent Heat

• Specific Heat Capacity (c): Heat needed to raise the temperature of 1 kg of a substance by 1 K ($Q=mc\Delta T$).
• Latent Heat (L): Heat absorbed/released during change of state at constant temperature ($Q=mL$).