Two Questions about thermal radiation....

In summary, the conversation discusses the apparent contradiction between the fact that heat travels from hot to cold bodies and that all things give out thermal radiation. The experts clarify that this is not a contradiction, as it is the net transfer of energy that matters. Additionally, they explain how the absorption of thermal radiation is affected by the surface texture of the absorbing body, with rough surfaces causing more absorption due to multiple reflections and smoother surfaces acting more like mirrors.
  • #1
Kaneki123
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Okay... I have two questions regarding thermal radiation...The first one is that, it is a constant fact that heat travels from hot to cold body, and all things give out thermal radiation, So arent these two facts contradictory in the sense that "everything is heating every other thing regardless of its temperature"?
My other question is that absorption of this radiation depends upon(alongwith other things) surface texture of the absorbing body, how so?
 
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  • #2
Kaneki123 said:
Okay... I have two questions regarding thermal radiation...The first one is that, it is a constant fact that heat travels from hot to cold body, and all things give out thermal radiation, So arent these two facts contradictory in the sense that "everything is heating every other thing regardless of its temperature"?
Why do you think it is a contradition? If you an I stand next to each other and start handing each other money, we are each enriching the other (and making ourselves poorer) at the same time. What matters is what is the ultimate balance. My preference is that you be the richer one and give me more money than I give you. Would that be a contradiction?
 
  • #3
Kaneki123 said:
Okay... I have two questions regarding thermal radiation...The first one is that, it is a constant fact that heat travels from hot to cold body, and all things give out thermal radiation, So arent these two facts contradictory in the sense that "everything is heating every other thing regardless of its temperature"?

Everything is transferring energy to everything else that its thermal radiation impacts, yes. But, as phinds stated, it is the net transfer that matters. A cold object will emit radiation that is absorbed by a hot object, but the hot object emits more radiation than the cold object. The cold object thus absorbs more energy over time and will heat up while the hot object will lose energy over time and cool down.

Kaneki123 said:
My other question is that absorption of this radiation depends upon(alongwith other things) surface texture of the absorbing body, how so?

A simple explanation just has to do with diffuse vs specular reflection. At the small scale, a rough surface reflects radiation in many different directions, some of which is absorbed by another nearby location which is lower/higher in surface height. In addition, some of the light penetrates into the material and is reflected and scattered by irregularities before emerging back out at a completely different angle than it entered at. Some materials, like felt, are used to line the inside of telescopes because all the fibers sticking out cause the light to undergo many different reflections. Upon each reflection a portion of the light is absorbed, leading to a large percentage of the light being absorbed instead of reflected.

In contrast, a very smooth surface acts like a mirror, reflecting the light back out at equal and opposite angle from the normal angle (normal angle is perpendicular to the surface). This effect is magnified as the angle of incidence increases and is nearly 100% when the angle approaches 90 degrees from normal (nearly parallel with the surface).

https://en.wikipedia.org/wiki/Reflection_(physics)
 

1. How is thermal radiation different from other types of radiation?

Thermal radiation is the type of electromagnetic radiation that is emitted by a hot body. It is different from other types of radiation (such as visible light or radio waves) because it is primarily dependent on the temperature of the emitting body, rather than its chemical composition or energy source.

2. What is the relationship between temperature and the amount of thermal radiation emitted?

The amount of thermal radiation emitted by a body is directly proportional to its temperature. This means that as the temperature of a body increases, the amount of thermal radiation it emits also increases.

3. How does thermal radiation transfer heat?

Thermal radiation transfers heat through electromagnetic waves. When these waves come into contact with an object, they are absorbed and increase the kinetic energy of the molecules in the object, causing it to heat up.

4. Can thermal radiation be reflected or absorbed?

Yes, thermal radiation can be both reflected and absorbed. The amount of radiation that is reflected or absorbed depends on the properties of the object it comes into contact with, such as its color, texture, and composition.

5. How is thermal radiation used in everyday life?

Thermal radiation is used in many everyday applications, such as cooking, heating, and generating electricity. It is also used in thermal imaging technology, which allows us to see the heat signatures of objects and living beings. Additionally, thermal radiation is used in medical treatments, such as infrared therapy, to help alleviate pain and inflammation.

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