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Thermal Radiation. By: Raghad Al Lawati and Magdah Al Sinaidi . G9 Block 1. Thermal Radiation. Energy is traveled in the form of electromagnetic waves, which includes infrared waves as well as light and they can travel through a vacuum (empty space).
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Thermal Radiation By: Raghad Al Lawati and Magdah Al Sinaidi. G9 Block 1
Thermal Radiation • Energy is traveled in the form of electromagnetic waves, which includes infrared waves as well as light and they can travel through a vacuum (empty space). • Warm objects radiate infrared, as the waves are invisible. If the object become hotter, they also emit shorter wavelengths which may include light. • The higher an object’s surface temperatures and the greater their surface area, the more energy they radiate per second.
Heat Radiation • Heat radiation can be detected using a thermopile and a blackened bulb meter. thermopile
Emitters and Absorbers • Black surfaces are better in emitting (sending out) thermal radiation than white surfaces. For example: a black saucepan cools down more quickly than a similar white one because it emits energy at a faster rate. • A good emitter of thermal radiation is also a good absorber, that means a black absorber is better than a similar white one. White or silvery surfaces are poor absorbers because they reflect most of the thermal radiation away.
Good and bad emitters and absorbers • Bad emitters and bad absorbers are objects that absorb heat radiation. They are silver. • Good emitters and good absorbers are objects that absorb heat radiation. They are black.
Green House effects • The atmosphere around us acts as a “heat trap” and this is because notably water vapour, carbon dioxide and methane absorb energy strongly at certain wavelengths in the infrared region of the spectrum. • The heat trapping action is called: the green house effect, and without it the surface of the earth would be 25° C. • It works when Thermal Radiation from the sun passes easily through the glass or plastic. The ground inside warms up and heats the air, but the hot air is trapped and cannot escape.
The Solar Panel • Some houses have a solar panel on their roof, it uses the sun’s thermal radiation to warm up water for the house. The blackened layer absorbs the radiant energy and warms up the water flowing through the pipes.
The Vacuum Flask • Vacuum flasks keep drinks inside hot or cold for hours, it has some features that helps in reducing the rate at which thermal energy flows out or in: • Insulated stopper to reduce conduction and convection. • Double walled container with a gap between the walls . • Walls with silvery surfaces to reduce thermal radiation.
