Transfer Of Thermal Energy
Visão Geral
A metal spoon in a hot drink soon burns your fingers, yet a wooden spoon stays cool. Warm air rises from a radiator to heat a whole room, and the Sun's warmth crosses the empty vacuum of space to reach us. These are the three ways thermal energy moves: conduction, convection and radiation.
In this topic you will describe experiments that reveal good and bad conductors, explain convection in terms of density changes, and learn how surface colour and texture affect infrared radiation. You will also see why an object stays at a steady temperature only when energy in balances energy out, and how that same balance controls the temperature of the Earth.
Objetivos
- Describe experiments to demonstrate the properties of good thermal conductors and bad thermal conductors (thermal insulators)
- Know that convection is an important method of thermal energy transfer in liquids and gases
- Explain convection in liquids and gases in terms of density changes and describe experiments to illustrate convection
- Know that thermal radiation is infrared radiation and that all objects emit this radiation
- Know that thermal energy transfer by thermal radiation does not require a medium
- Describe the effect of surface colour (black or white) and texture (dull or shiny) on the emission, absorption and reflection of infrared radiation
- [Supplement] Describe thermal conduction in all solids in terms of atomic or molecular lattice vibrations and also in terms of the movement of free (delocalised) electrons in metallic conductors
- [Supplement] Describe, in terms of particles, why thermal conduction is bad in gases and most liquids
- [Supplement] Know that there are many solids that conduct thermal energy better than thermal insulators but do so less well than good thermal conductors
- [Supplement] Know that for an object to be at a constant temperature it needs to transfer energy away from the object at the same rate that it receives energy
- [Supplement] Know what happens to an object if the rate at which it receives energy is less or more than the rate at which it transfers energy away from the object
- [Supplement] Know how the temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted from the Earth’s surface
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- Which method of thermal energy transfer can occur through a vacuum? A. conduction B. convection C. radiation D. none of these Answer: C
- Metals are good thermal conductors mainly because they contain: A. large atoms B. free electrons C. trapped air D. water Answer: B
- Warm fluid rises in convection because it becomes: A. denser B. less dense C. heavier D. solid Answer: B
- Which surface is the best emitter of infrared radiation? A. shiny silver B. polished white C. dull black D. shiny white Answer: C
- For an object to stay at a constant temperature, the energy it receives must be: A. greater than energy lost B. equal to energy lost C. less than energy lost D. zero Answer: B
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Conduction
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Radiation
You can feel the heat transfer from a fire and from the Sun. Similarly, you can sometimes tell that the oven is hot without touching its door or looking inside—it may just warm you as you walk by. The space between the Earth and the Sun is largely empty, without any possibility of heat transfer by c
"College Physics: Radiation" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/14-7-radiation. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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