(455) Thermal energy transfer [IB Physics SL/HL]

Introduction to Thermal Energy

• Thermal energy (Q) is the transfer of heat, measured in joules.

• Heat moves from hot to cold through three key mechanisms: conduction, convection, and radiation.

Thermal Conduction

• Definition: Transfer of energy without bulk movement of particles.

• Example: Holding a metal rod at one end; heat travels along the rod.

• Mechanism: Vibrating particles transfer kinetic energy to neighboring particles.

  • Free Electrons in metals carry heat effectively.

• Key Concept: Thermal conductivity; it influences how well a material transfers heat.

Thermal Conductivity Equation

• Formula: [ \frac{\Delta Q}{\Delta t} = K \cdot A \cdot \frac{\Delta T}{\Delta X} ]

  • (\Delta Q): Heat transferred (joules)

  • (\Delta t): Time (seconds)

  • A: Cross-sectional area (m²)

  • (\Delta T): Temperature difference (Kelvin or Celsius)

  • (\Delta X): Thickness of material (meters)

• Units of Thermal Conductivity (K): [ \text{watts} \cdot ext{m}^{-1} \cdot ext{K}^{-1} ]

Thermal Convection

• Definition: Transfer of energy through the bulk movement of particles, primarily in fluids.

• Example: Hot air rises; cooler air descends, creating a convection current.

• Scenario: In a heated room, hot air from a heater rises, pulling in cooler air which replaces it.

• Natural Phenomenon: Sea breeze and land breeze driven by temperature differentials of land and water.

Thermal Radiation

• Definition: Transfer of energy through electromagnetic radiation (light) without requiring a medium.

• Example: sunlight warming a room.

• Properties of Light: Different wavelengths affect materials differently (e.g., ultraviolet can cause sunburn, microwaves heat water via molecular vibration).

• Key Concept: Light can transfer energy even in a vacuum, unlike conduction and convection.

Summary of Thermal Energy Transfers

• Conduction: Happens without particle movement; relies on energy transfer between particles.

• Convection: Involves the movement of particles and is common in liquids and gases.

• Radiation: Involves electromagnetic waves and does not require a physical medium to transfer energy.