P1.1 Energy Transfer By Heating Summary

Infrared Radiation: The transfer of energy by electromagnetic waves. All objects emit it, the more infrared radiation it emits the hotter the object is.

Dull Black: good absorber, poor reflector, good emitter

Light Shiny: poor absorber, good reflector, poor emitter

In a solid particles vibrate about a fixed position.

In a liquid, particles are in contact but move at random.

In a gas, particles are far apart and move fast at random.

Conduction: When one end of a solid is heated th particles at that end gain kinetic energy and vibrate more. This energy is passed on to neighbouring particles and in this way the energy is transferred. Metals have free electrons which help to transfer energy.

Convection: As fluid near the heat source warms, it expands, becomes less dense and rises. the rising fluid is replaced by cooler fluid which in turn warms and rises. As the fluid moves away from the heat source it cools down, becomes more dense and descends. Eventually a convection current is set up.

Evaporation: Evaporation takes place when the most energetic liquid molecules escape from the liquids surface and become a gas. The average kinetic energy of the remaining molecules is less so the temperature decreases. Increase rate of evaporation by increasing temperature, surface area or flow of gas above liquids surface.

Condensation: Gas to Liquid. Increase rate of by increasing surface area or reducing surface temperature.

Greater temperaure difference = Greater rate of energy transfer

Maximise energy transfer: good conductore, dull black, lots of airflow

Minimise energy transfer: good insulator, white and shiny, trapping air in small pockets

In a vacuum flask... Plastic Cap and container- conduction and convection

Inside silvered surfaces- radiation

Vacuum- conduction and convection

E=m x c x o

Lower u-valve = Better Insulator