Physics #2

Conduction

Conduction is a type of heat transfer that occurs in solids, especially metals, when particles are tightly packed. When part of the solid is heated, the particles in the area gain energy, vibrate more and pass this energy to neighbouring particles through collisions.

Convection

Convection is a type of heat transfer that occurs in fluids (liquids or gases). When a fluid is heated, the particles move faster and spread out, causing fluid to become less dense. The warmer less dense rises, while the cooler, denser fluid sinks to take its place. This movement creates a convection current that transfers heat throughout the fluid.

Radiation

Radiation is a type of heat transfer through infrared radiation (which carries heat energy) and it does not need particles, so it can happen in a vacuum. (like space). All objects emit infrared radiation, but hotter objects emit more. Surfaces affect how well heat is absorbed or emitted. Dull, black surfaces absorb and emit radiation better than shiny, white surfaces, which reflect it.

Radiation (Black + White Objects) 

• Black Object: Absorbs most radiation → surface heats quickly.Heat conducts through object. Strong IR emitter → heats air + water faster. Also absorbs IR from hot water. Good radiator → loses heat fast → water cools quickly.

• White Object: Reflects most radiation → little absorbed → heats slowly. Weak heat conduction into object Weak IR emitter → poor radiator. Removes heat slowly → water heats slowly + cools slowly.

Heat Transfer Prevention

Conduction: Insulators (plastic, foam, wood), air gaps, double glazing, clothing layers. These materials have low thermal conductivity → particles do not pass energy easily, and air gaps reduce collisions → slows heat flow.

Convection: Lids, sealed containers, draught-proofing, insulation that traps air (wool, fibreglass). Prevents air/fluid movement. Trapped air cannot circulate, so no convection currents can form.

Radiation: Shiny or light-coloured surfaces, foil insulation, reflective linings. Shiny/light surfaces reflect IR and emit very little IR, reducing heat absorption and emission.

Latent Heat Stages

Latent Heat of Fusion (Melting / Freezing): Temperature stays constant while a solid becomes a liquid (or liquid → solid). All added/removed energy is used to break or form bonds between particles, not to change temperature.

Latent Heat of Vaporisation (Boiling / Condensing): Temperature stays constant during liquid → gas (or gas → liquid). Energy goes into breaking or forming intermolecular bonds so particles can separate or come together — again, no temperature change.