In what direction is thermal radiation emitted?

In summary, thermal vibrations of molecules in a solid or crystal can produce thermal radiation in preferred directions, as seen in the emission of photons from a dielectric material in a simple capacitor when an electric field is applied. The choice of dielectric material can affect the concentration of emitted photons.
  • #1
Lewis R
3
0
It is well known that thermal vibrations of molecules produce thermal radiation or photons (infrared and visible): but in what directions?
I can understand in a gas or liquid the molecules will be rotating in all directions somewhat uniformly and, thus, photon emission will be uniform in all directions (diffuse). But in a solid or crystal, with the molecules being restrained somewhat, would not the photon emission be in preferred directions?
Specifically, construct a simple capacitor - two metal plates separated by a dielectric material. The dielectric material will emit thermal photons in a diffuse manner from its surfaces not covered by the metal plates (i.e. from the edges of the capacitor). If a low DC voltage ( up to 100 volts) is applied to the plates, will the dielectric molecules rotate to align with the electric field and, thus, emit photons in a more concentrated manner,hopefully parallel to the metal plates? And what dielectric would be best for this result? Thanks
 
Science news on Phys.org
  • #2
Yes, the thermal photons emitted from a dielectric material such as a capacitor will be concentrated in the direction of the electric field. The molecules of the dielectric material will align with the electric field and so will emit photons in a more focused and parallel manner. The dielectric material that is best for this result would depend on the application and the desired properties, but some common dielectrics used in capacitors include polyester, polyethylene, polypropylene, and paper.
 
  • #3


I can provide some insight into the direction of thermal radiation emission. Thermal radiation is emitted in all directions, regardless of the state of matter (solid, liquid, or gas). This is because thermal radiation is a result of the random motion and vibrations of molecules, which occur in all directions.

In a gas or liquid, as you mentioned, the molecules are able to move more freely and therefore emit radiation in all directions. In a solid or crystal, the molecules are more closely packed and have less freedom to move, but they still emit radiation in all directions due to their thermal vibrations.

In regards to your question about a simple capacitor, the dielectric material will emit thermal photons in a diffuse manner from its surfaces not covered by the metal plates, as you stated. Applying a low DC voltage may cause the molecules in the dielectric to align with the electric field, but this would not necessarily result in a more concentrated emission of photons. The emission of thermal radiation is still a result of random molecular motion and would not be significantly affected by the electric field.

As for the best dielectric material for this result, it would depend on the specific properties and composition of the material. Some materials may have a higher thermal conductivity, which could affect the emission of thermal radiation. It would require further experimentation and analysis to determine the most suitable dielectric material for this purpose.

I hope this helps to clarify the direction of thermal radiation emission and the potential effects of an electric field on it.
 

Related to In what direction is thermal radiation emitted?

1. What is thermal radiation?

Thermal radiation is the emission of electromagnetic waves from a material's surface due to its temperature. It is a form of heat transfer and is also known as infrared radiation.

2. What direction is thermal radiation emitted?

Thermal radiation is emitted in all directions from the surface of the material. However, the intensity of the radiation is dependent on the temperature and properties of the material.

3. Does thermal radiation travel in a straight line?

Yes, thermal radiation travels in a straight line until it is absorbed or reflected by another material. This is known as the inverse square law, where the intensity of the radiation decreases as the distance from the source increases.

4. What factors affect the direction of thermal radiation?

The direction of thermal radiation is affected by the temperature and surface properties of the material. The shape and orientation of the material's surface can also influence the direction of thermal radiation.

5. How does thermal radiation differ from other forms of heat transfer?

Unlike conduction and convection, thermal radiation does not require a medium to transfer heat. It can travel through a vacuum and does not depend on the temperature difference between two materials. Additionally, thermal radiation can be reflected or absorbed by different materials, while conduction and convection only transfer heat through direct contact.

Similar threads

Replies
5
Views
811
Replies
1
Views
1K
  • Thermodynamics
Replies
20
Views
10K
  • Thermodynamics
Replies
16
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
7
Views
1K
  • Thermodynamics
Replies
9
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
  • Atomic and Condensed Matter
Replies
3
Views
2K
Replies
3
Views
962
Replies
4
Views
1K
Back
Top