Emissivity of radiation from a surface, Leslies cube

[rayman123]

Homework Statement

Hello! I am going to do a demonstration involving the Leslie's cube to demonstrate the emissivity of a thermal radiation from different surfaces. I have been reading some about black body radiation which has emissivity = 1 but this is not the case. Leslie's cube has 4 surfaces but could someone explain to me why the black surface emitts the most of the radiation and the silver one least?

Thank you!

Homework Equations

The Attempt at a Solution

 

[Antiphon]

Black surfaces absorb, silver or white surfaces reflect.

The absorption and emission processes are symmetrical. This means a good absorber is a ready emitter.

For the white or silvet surface pretend the energy to be emitted is just inside the cube. The silver surface will reflect the energy back into the box, so low emissivity.

 

[rayman123]

yes I know that but I would like to know what is the physical explanaition for it? what makes that the black one emitts the most? why it has the highest emissivity ?

 

[drames88]

i just did experiment on Leslie's cube, but can not often answer 1 question: which says, what is the advantage and disadvantage of my device in every day life situation. can someone please help me with this!

 

[paranormal]

Hello there!

The emissivity of a surface refers to its ability to emit thermal radiation. It is a measure of how efficiently a surface can emit radiation as compared to a black body, which is a theoretical object that absorbs all radiation incident on it and emits radiation at the maximum possible rate for a given temperature.

In the case of Leslie's cube, the black surface has an emissivity of 1 because it is designed to absorb and emit radiation as efficiently as a black body. This means that it will emit the most radiation compared to the other surfaces, which have lower emissivity values. The silver surface, on the other hand, has a lower emissivity because it is a good reflector of radiation and does not absorb or emit it as efficiently as the black surface.

In general, the emissivity of a surface depends on its material properties, surface finish, and temperature. Different materials have different abilities to emit radiation, and surfaces with rougher finishes tend to have higher emissivity values because they have a larger surface area to emit radiation from. Additionally, the emissivity of a surface increases with temperature, which is why the black surface of Leslie's cube, which is designed to absorb and emit radiation efficiently, will emit more radiation compared to the other surfaces at the same temperature.

I hope this helps to explain why the black surface of Leslie's cube emits the most radiation and the silver one emits the least. Let me know if you have any other questions. Good luck with your demonstration!