thermal energy

2.3 Transfer of Thermal Energy

• Conduction

  • Conduction is the flow of thermal energy through matter from places of higher temperature to places of lower temperature without movement of the matter as a whole.

• Mechanism of Thermal Conduction in Solids

  • Atoms vibrate and transfer thermal energy through local vibrations.

  • Metals, like aluminum and copper, conduct heat through free electrons.

• Characteristics of Conductors vs Insulators:

  • Metals: Good conductors (e.g., saucepan) conduct heat quickly.

  • Poor conductors (e.g., plastic) can be used for handles to keep cool.

• Experiments Demonstrating Conductivity:

  • Conductivity comparison using metals and wax melting point tests (e.g., copper, brass, iron).

2.3.2 Convection

• Definition and Principles:

  • Thermal energy transfers in liquids/gases via convection, involving fluid motion.

• Heating and Density:

  • Warmer fluids expand, become less dense, and rise while cooler fluids sink, creating convection currents.

• Experimental Demonstration:

  • Use of potassium permanganate in heated water shows convection currents.

• Examples:

  • Convector heaters and natural convection currents causing sea breezes.

2.3.3 Radiation

• Nature of Thermal Radiation:

  • Thermal radiation is infrared and does not require a medium.

• Emissivity:

  • Dull black surfaces are good absorbers/emitter of thermal radiation; shiny surfaces reflect it well.

• Factors Affecting Radiation:

  • Surface temperature and area affect emission rate.

• Practical Applications:

  • Use of reflective surfaces in buildings to mitigate heat transfer.

2.3.4 Consequences of Thermal Energy Transfer

• Energy Loss in Buildings:

  • Main losses occur through conduction in walls, roofs, and windows.

  • Energy-saving measures include insulation techniques to minimize energy loss.

• Applications of Conductors and Insulators:

  • Good conductors like metals are used in cooking, whereas insulators (e.g., wool, polystyrene) maintain temperature for liquids.

2.3 Applications of Thermal Energy Transfer

• Ventilation Systems:

  • Heating systems must compensate for energy loss and warm incoming air to maintain comfort.

• Types of Energy Transfer in Real Life:

  • Everyday heating applications demonstrate conduction, convection, and radiation.