7. Conduction, Convection & Radiation | How Heat Energy is Transferred

1. Conduction

The Process

• Particle Vibration: Heat energy is transferred through collisions between neighboring vibrating particles.

• Mechanism: When one end of a solid is heated, the particles gain kinetic energy and vibrate more. These vibrations cause collisions with adjacent particles, passing the energy along the object.

• Medium: Occurs primarily in solids because particles are closely packed, making collisions frequent and efficient.

Thermal Conductivity

• High Thermal Conductivity: Materials like metals (copper, aluminum) transfer heat quickly.

• Low Thermal Conductivity (Insulators): Materials like wood, plastic, and air transfer heat slowly.

• Practical Use: Plastic handles on mugs or pans act as insulators to prevent heat from reaching your hand.

2. Convection

The Process

• Fluid Movement: Heat transfer occurs through the physical movement of particles in fluids (liquids and gases).

• Mechanism: 1. Particles near a heat source gain kinetic energy and move faster.

  2. They spread out, causing the heated fluid to become less dense.

  3. The less dense, warm fluid rises above the cooler, denser fluid.

  4. As it rises, it cools, becomes denser again, and sinks.

• Convection Currents: This repeating cycle of rising and sinking is called a convection current (e.g., heating water in a pot or air in a room).

3. Radiation

The Process

• Wave-Based Transfer: Heat energy is transferred via infrared waves rather than particles.

• No Medium Required: Radiation can travel through a vacuum (empty space). This is how heat from the Sun reaches the Earth.

• Emission and Absorption: * All objects emit and absorb infrared radiation, regardless of temperature.

  • Hotter objects emit more radiation than cooler ones.

  • The temperature of an object depends on the balance between the radiation it absorbs and the radiation it emits.

4. Summary Table of Heat Transfer