Heat & Its Effects and Transfer of Thermal Energy

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Heat & Its Effects and Transfer of Thermal Energy
1 Movement of Thermal Energy
1.1 flows from a region of higher temperature to a region of lower temperature
1.2 Thermal energy transfer
1.2.1 Conduction Thermal energy transfer through a medium or material from one particle to another All matter are conductors of thermal energy Good conductors Poor insulators Metals Solids (fastest conductor) Poor conductors Good insulators Non-metals Liquids & Gases
1.2.2 Convection Thermal energy transfer by movement of fluids (liquids & gases) Happens only in liquids & gas ( fastest in gas) Expansion of heated liquids & gas Volume increases Mass remains the same Density decreases Convection current When a fluid is heated, it expands. It will become less dense and rises. Cooler fluid, which is denser, will sink to replace the warm fluid.
1.2.3 Radiation Thermal energy transfer in the from of waves, without a medium Happens in all matter & vacuum Total surface area of the body Larger surface area radiates/absorb thermal energy faster Temperature of the body Hotter body radiates faster Nature of the surface of the body Black, rough, dull (good absorber/radiator) White, smooth, shiny (Good reflector) All objects emit infra-ray radiation and all objects absorb it. Different objects emit and absorb infra-ray radiation at different rates
2 Uses of Expansion & Contraction
2.1 Bimetallic Strips
2.1.1 Two different strips riveted or welded together
2.1.2 Brass expands/contracts more than Iron when heated
3 Expansion & Contraction
3.1 When a matter is heated it increases in volume and expands
3.2 When a matter is cooled, it decreases in volume and contracts
3.3 Fastest in gas, slowest in solids
3.4 When a body expands or contracts, large forces may be set up
3.4.1 Effects Cracking in roads and pavements Warping in MRT and railway Snapping telephone wires Cracked glassware Cracked water pipes Bridges may damage
3.4.2 Solutions Expansion gaps (cracks in road & warped MRT) Telephone wires strung loosely Pyrex glass (expands very little when heated) Rollers (damaged bridges) Expansions bends (water pipes)
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