Physics Chapter 8 - Thermal Process

Thermal Equilibrium

Heat flows from a hotter region to a cooler region until both reach the same temperature; No net heat transfer occurs when thermal equilibrium is reached

Conduction (in solids)

Transfer of heat without movement of the material as a whole; Atoms/molecules vibrate faster when heated → transfer kinetic energy to neighbouring particles through collisions; In metals, free electrons move and transfer energy faster (good conductors); Examples: Metal spoon heating in hot water, Cooking on a pan

Good Conductors

Metals such as copper and aluminium; transfer heat efficiently

Poor Conductors (Insulators)

Materials such as wood, plastic, glass; transfer heat poorly

Convection (in liquids & gases)

Heat transfer due to movement of the fluid itself; Fluid near heat source warms → particles move faster → density decreases → warmer fluid rises; Cooler, denser fluid sinks → sets up a convection current; Examples: Sea breeze, boiling water, room heating

Radiation

Heat transfer via electromagnetic waves (infrared); Does not require a medium (can occur in vacuum)

Rate of radiation depends on

• Surface colour & texture: dull, dark surfaces are best absorbers/emitters; shiny, light surfaces are poor absorbers/emitters

• Surface temperature: higher temperature → greater rate of radiation

• Surface area: larger surface → faster radiation
  Examples: Sun’s heat reaching Earth, cooling fins on engines, vacuum flasks