Radiant Heat Energy: Why is Hand Protected Behind Glass?

AI Thread Summary
Placing a hand behind glass does not allow it to feel radiant heat from a fireplace because glass is transparent to visible light but blocks infrared radiation, which carries heat. This phenomenon contrasts with sunlight, where glass allows infrared radiation to pass through, enabling heat sensation. The discussion highlights the greenhouse effect, where barriers like glass trap heat by allowing visible light in while preventing infrared radiation from escaping. This principle explains why energy enters during the day and is retained at night, leading to a temperature increase. Understanding these radiation spectra differences is crucial for grasping the relationship between heat transfer and the greenhouse effect.
westdivo
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why does your hand not feel the radiant heat energy from a fireplace if you place it behind a sheet of glass, even though you can see the fire very easily?
 
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I've never noticed that. Do you know the greenhouse effect?
 
Really? I doubt it.
Why can my hand feel the radiant heat from the sun if we place it under glass?

And what is the relation between the question and the greenhouse effect?
 
zlbeidou said:
what is the relation between the question and the greenhouse effect?

If you have a barrier (glass or atmosphere) that is opaque to infrared but transparent to visible light, it will let plenty of energy in during the day, and still block much of the heat-loss during the night. (The key is the differences between the radiation spectra from either side.)
 
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