Conduction, convection and radiation

Energy flow [Thermal transfer]
high temperature -> low temperature

- Conduction
- Thermal conductors - materials that allow thermal energy to transfer through them quickly
- Thermal insulators don't
- One end of the conductor is heated
- Atoms that make up its structure vibrate vigorously
- Atoms linked together - increased vibration passed on to other atoms
- Kinetic energy passes through the whole material

- Metals are good conductors
- Contain freely moving electrons
- Transfers energy rapidly
- Electrons travel all over the metal - take thermal energy with it
- Vacuum is perfect insulator

- Convection
- Occurs in liquids and gases
- Material flows ('fluids')
- Heated
- Energy transferred to particles
- Move faster and further apart
- Heated fluid less dense than unheated fluid
- Less dense fluid rises above the more dense (colder) fluid
- Fluid circulates
- [Convection current] - How thermal energy is transferred
- Insulators (ceiling tiles etc.) contain trapped air pockets to prevent air from circulating and transferring thermal energy by convection

- Radiation
- Does not need particles
- Can travel through vacuum
- Radiated heat energy carried mainly by infrared radiation
- Hot objects radiate more infrared than cold objects

- Dull black surface - Good emitter and good absorber
- Bright shiny surface - Poor emitter and poor absorber

- Leslie's cube - Different surfaces (shiny, dull, etc) to show how they emit and absorb thermal radiation at different rates