Chapter 15: Thermal Energy and Heat

Conduction

The transfer of thermal energy through direct contact between particles in a solid.

Convection

The transfer of thermal energy through the movement of fluids or gases caused by differences in density.

Radiation

The transfer of thermal energy through electromagnetic waves, which can occur in a vacuum.

Mechanisms of Heat Transfer

• Conduction: Occurs in solids where particles vibrate and transfer energy to neighboring particles.
• Convection: Creates currents within fluids, where warmer regions rise and cooler regions sink.
• Radiation: Does not require a medium and can transfer energy through empty space (e.g., sunlight).

Applications of Heat Transfer

• Conduction: Used in cooking utensils made of metals that quickly transfer heat.
• Convection: Basis of weather patterns and HVAC systems.
• Radiation: Heat from the Sun warming the Earth.

Heat Transfer Equations

Fourier's Law (Conduction)

$Q=k\times A\times \frac{\mathrm{\Delta T}}{d}$

Newton's Law of Cooling (Convection)

$Q=h\times A\times (T$_surface - T _ambient )

Questions for Students

1. Define conduction, convection, and radiation, and provide one example of each.
2. Explain how convection currents are formed in fluids.
3. Why can radiation transfer energy through a vacuum, while conduction and convection cannot?
4. What role does conduction play in cooking? Provide an example.
5. Calculate the heat transfer rate using Fourier's Law for a metal rod with a cross-sectional area of 0.01 m², a temperature difference of 50 °C, and a length of 0.5 m. Use k = 200 W/m⋅°C.