Question
Discuss Ferry’s construction for a prefect black body.
Solution
Ferry’s black body consists of a hollow double-walled sphere which is blackened inside. The sphere has a small hole on its surface.
Directly opposite to hole, there is a wedge shaped structure inside the sphere.
Ferry's black body is shown below,
When the radiations of any wavelength enter the hole, they hit the wedge and suffer a number of reflection at the inner wall of sphere until the radiations are completely absorbed.
Thus, the small hole acts as a black body absorber. To make it black body radiator, the cavity is heated.
It is observed that radiations come out from the hole.
Directly opposite to hole, there is a wedge shaped structure inside the sphere.
Ferry's black body is shown below,
When the radiations of any wavelength enter the hole, they hit the wedge and suffer a number of reflection at the inner wall of sphere until the radiations are completely absorbed.
Thus, the small hole acts as a black body absorber. To make it black body radiator, the cavity is heated.
It is observed that radiations come out from the hole.
