Question

Draw a neat labelled diagram for Ferry’s perfectly black body.

Answer 1

Hint: A cavity with double sided walls made up of any substances, with a small aperture is said to be an excellent black body. This is known as Ferry's black body. It can also absorb all electromagnetic radiation fallen on it without depending on the wavelength.

Complete answer:
Let us discuss the design of ferry’s blackbody. The inside surface of this type of black body should be black. And also we need to have enough reflections to take place, by that way each and every incident light will get absorbed in the spectrum by this blackbody. This will be smoothly working in some of the microscopic structures as they have a lot of small cavities that can absorb, re-emit and scatter the light. Ferry's black body is made with a hollow double-walled sphere which will be perfectly blackened inside. The dual wall is made up so that inside of it will be at uniform temperature although different parts of the outside are getting different sources of heat. The sphere is having a minute hole on its surface. There it has been placed on the opposite side a wedge-shaped structure inside the sphere for initialising reflection. When the radiations of any range of wavelength gets into the aperture, it incidents on the wedge and undergoes multiple reflections on the inner wall of the black body up to which the radiations are completely absorbed. Therefore, the small hole is said to be the black body absorber. The diagram for the Ferry’s black body is given below:

Therefore the answer for this question is obtained.

Note:
A blackbody has a spectrum that is dependent only on temperature. The simplest way to get this condition is to have a body where the light comes only from the scattering of black substance at a uniform temperature. The Ferry black body is designed so no ray coming in from the outside can get out again. Therefore if you have a reflection of the sunlight you don't get any sunlight out.