Question

What is a perfectly black body? Explain Ferry’s black body.

Answer 1

Hint: A physically existing body that can absorb all the radiation incident on it is called a black body and based on the percentage of absorption of the incident light, Ferry’s black body comes into picture being nearest to an ideal black body.

Complete answer:
An idealized physical body, which can absorb all the electromagnetic radiations when incident on it irrespective of its frequency or incident angle is known as a black body. At constant temperature, the black body emits electromagnetic radiation known as black body radiation which follows Planck's law and thus it has a spectrum which is dependent on temperature alone.
At thermal equilibrium, a black body exhibits two notable properties,
it emits almost equal to or more thermal radiative energy at every frequency than any other body keeping the temperature constant,
The energy emitted by the black body is independent of direction and radiates energy isotropically.
Although, we cannot realise a perfect black body in practice. Ferry’s black body is considered as the nearest best example of an ideal black body. It is generally a doubled wall, where the outer one is nickel-coated and the inner one is blackened completely and in between these two walls, vacuum is present so as to prevent heat loss that can happen due to conduction and radiation. The incident radiations enter into these vessels through the hole and a conical projection is made just in front of the hole inside the black body so as to trap the incident radiations.

The black body can start emitting electromagnetic radiations, once it is heated at high temperature.

Additional information:
On the contrary of a black body, white body is also there having a rough surface and reflects all the incident rays completely in all directions uniformly.
Black holes are a spacetime region from which nothing can escape. Around a black hole, a surface which has been defined mathematically is called an event horizon and is considered as the point of no return.

Note:
The term blackbody radiation is also used to describe the relation between the wavelength and temperature of the object. A black body, according to its temperature, emits the radiations in a continuous spectrum. This is the main reason behind the different colors of stars, like red stars are mostly cooler, so they emit wavelengths equivalent to that of red color.