Emissivity as a function of wavelength

In summary, the experiment involved a Leslie Cube with one black and one white face, hot water, and measuring the Irradiance of thermal radiation. Despite the white face having a higher emissivity in the visible wavelengths, both faces had similar emissivities in the infrared spectrum. This is because color does not affect a material's ability to absorb and emit thermal radiation, only visible wavelengths. The question of reflected radiation from external sources was also raised.
  • #1
yellowputty
9
0

Homework Statement



Hello, I'm a little confused. I did an experiment today with a Leslie Cube. One of the faces was a black paint, and another a white paint. I know that white reflects well and has a low emissivity, at least in the visual wavelengths. In the Leslie's cube, was hot water, so I was measuring the Irradiance of thermal radiation. From the results I concluded that the white and black faces had similar emissivities (in fact the white face was slightly higher). I understand that emissivity depends on several factors, temperature, angle and also wavelength. How come in the infrared spectrum, both faces have similar emissivities? I have a feeling the answer lies in a blackbody diagram. Can someone point me in the right direction?

Thanks in advance :)
 
Physics news on Phys.org
  • #2
I think I just worked it out. Colour has nothing to do with a materials ability to absorb and hence emit thermal radiation. Colour is important in reflecting and absorbing wavelengths in the visible spectrum only. A white material will reflect all visible wavelengths, but a black surface would absorb all, and re-emit as thermal radiation.

I think oberlooked the way that visible light is then turned into thermal radiation. Thank you!
 
  • #3
You may be correct. I thought of another problem. Maybe you are measuring reflected radiation that the cube reflects from external sources? How have you isolated this?
 

1. What is emissivity as a function of wavelength?

Emissivity as a function of wavelength refers to the relationship between the emissivity of a material and the wavelength of the radiation it emits. Emissivity is a measure of how well a material emits thermal radiation, and it varies with the material's composition, surface properties, and temperature.

2. How does emissivity change with wavelength?

Emissivity typically follows a bell-shaped curve as a function of wavelength, with a peak at a specific wavelength. This peak wavelength is determined by the material's physical properties and temperature. At shorter wavelengths, emissivity tends to decrease, while at longer wavelengths, it tends to increase.

3. Why is emissivity as a function of wavelength important?

Understanding emissivity as a function of wavelength is crucial in various fields of science and engineering. It is essential for accurately predicting the thermal radiation emitted by objects, which is important in fields such as thermodynamics, astrophysics, and materials science.

4. How is emissivity as a function of wavelength measured?

Emissivity as a function of wavelength is typically measured using spectrophotometers, which can measure the amount of radiation emitted at different wavelengths. These measurements are then used to plot the emissivity curve for a particular material.

5. Can emissivity as a function of wavelength be controlled?

Yes, emissivity as a function of wavelength can be controlled to some extent by altering the material's surface properties or temperature. This is important in applications where controlling thermal radiation emissions is necessary, such as in heat transfer or energy conservation.

Similar threads

Replies
3
Views
243
  • Materials and Chemical Engineering
Replies
2
Views
1K
Replies
8
Views
2K
  • Quantum Physics
Replies
23
Views
2K
  • Advanced Physics Homework Help
Replies
4
Views
6K
Replies
29
Views
2K
Replies
7
Views
1K
  • Quantum Physics
Replies
18
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
906
  • Thermodynamics
Replies
8
Views
1K
Back
Top