IGCSE 0625 · THERMAL · 2.3

Transfer of thermal energy

Conduction, convection, and radiation: how each one works and how we use and control them. It builds on the particle model and temperature, links to the infrared part of the electromagnetic spectrum, and points on to insulation, efficiency, and the Earth's energy balance.

TOPIC 2.3: TRANSFER OF THERMAL ENERGY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 2.1 Particle model 2.2 Temperature & energy 3.3 Infrared (EM) LEADS TO Insulation & efficiency Earth's energy balance 6 Stars & radiation ENERGY TRANSFER 1 · CONDUCTION Energy passes through solids as particles vibrate and knock into their neighbours. Metals conduct best: free electrons carry energy quickly through the metal. Non-metals, liquids, and gases are poor conductors, so they make good insulators. energy flows to the cooler end 2 · CONVECTION In liquids and gases, heated fluid expands, becomes less dense, and rises. Cooler, denser fluid sinks to take its place. This circulation is a convection current. It carries energy through the whole fluid. heat source 3 · RADIATION All objects emit infrared radiation, part of the electromagnetic spectrum. It needs no medium. hot object black, dull: good shiny, white: poor Dark, dull, rough surfaces are the best emitters and absorbers of radiation. Shiny, white, smooth surfaces are poor emitters and good reflectors. Works through a vacuum, so it reaches us from the Sun across empty space. 4 · USING & CONTROLLING TRANSFER A vacuum flask is designed to reduce all three ways that energy is transferred. hot stopper Vacuum gap: no particles, so no conduction or convection. Silvered walls reflect radiation back in. Stopper blocks convection and evaporation at the top. The same ideas explain home insulation, heating systems, and the Earth's energy balance.
TOPIC 2.3: TRANSFER OF THERMAL ENERGY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 2.1 Particle model 2.2 Temperature & energy 3.3 Infrared (EM) LEADS TO Insulation & efficiency Earth's energy balance 6 Stars & radiation ENERGY TRANSFER 1 · CONDUCTION Energy passes through solids as particles vibrate and knock into their neighbours. Metals conduct best: free electrons carry energy quickly through the metal. Non-metals, liquids, and gases are poor conductors, so they make good insulators. energy flows to the cooler end 2 · CONVECTION In liquids and gases, heated fluid expands, becomes less dense, and rises. Cooler, denser fluid sinks to take its place. This circulation is a convection current. It carries energy through the whole fluid. heat source 3 · RADIATION All objects emit infrared radiation, part of the electromagnetic spectrum. It needs no medium. hot object black, dull: good shiny, white: poor Dark, dull, rough surfaces are the best emitters and absorbers of radiation. Shiny, white, smooth surfaces are poor emitters and good reflectors. Works through a vacuum, so it reaches us from the Sun across empty space. 4 · USING & CONTROLLING TRANSFER A vacuum flask is designed to reduce all three ways that energy is transferred. hot stopper Vacuum gap: no particles, so no conduction or convection. Silvered walls reflect radiation back in. Stopper blocks convection and evaporation at the top. The same ideas explain home insulation, heating systems, and the Earth's energy balance.
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