Question

Make a mindmap that contain:

a-Types of radiation body and surfaces - Search on the black body, gray body, real body, opaque medium and diffuse surface. Describes them (using keywords) and give example when/where they occurs.
b-Radiative processes and properties - Search on the emissivity (include type of surface emission and emissive power), irradiation, radiosity, absorptivity, reflectivity, transmissivity. Describes them (using keywords) and if possible, give example when/where they occurs.

Answer 1

Answer:

(a): Radiation is the energy which is obtained from the unstable atoms which undergoes the radioactive decay.Radiation is form of energy which travels from the source and it is found in different form and different kinds of radiations are available.

Black body:

All the matters present in the environment emits the radiation when the temperature of the matter is above absolute zero. Radiation is known as the conversion of internal energy of body in to electromagnetic energy. That why it is also known as thermal radiation.

All matters presents on the earth, absorbs the electromagnetic radiation to some extent.

The object which absorbs all the radiation falling on the surface of it, at all the wave lengths is known a Black body. Radiation which takes place during the absorbtion of heat, is called black body radiation.

When and where black body is used:

The black bodies are used in various application an at different point of times as black bodies are used in heating, thermal imaging, lighting and testing and measurement application The black bodies are used for lighting, heating, security, thermal imaging, as well as testing and measurement applications.Intensity of energy at any point of temperature can be found with the help of planks law, so black body is also used for the testing and calibration of  the radiation thermometers

Gray body

A gray body is known as the imperfect black body. Gray bodies partially absorbs the radiation which is incident on the surface.The ratio of gray body thermal radiation and black body thermal radiation is called and known as emissivity of the gray body.

When and where Gray body is used:

Gray body applications can be seen in the pyrometers, remote sensing elements

Real body

Real bodies or objects are the bodies which never behaves like full ideal black body as in nature there is no body which is perfectly black. Emmisivity also tells about material that how well a real body can radiate the energy when it is compared with the real bodies. Emmisivity depends upon wavelength temperature of the surface .and wavelength. But according to gray body assumption radiation do not belongs to wavelength.

When and where Real body is used:

All bodies which are available on the earth are mostly real bodies as there is no body which absorbes the 100% radiation as well there is no bodies which will emit the 100% radiation out of it. So the use of real bodies in general application and mostly all the major radiation heat transfers application.

Opaque medium

An opaque medium is the medium which is not transparent as also it is not translucent (in which some light can pass). Whenever there is an instance where light falls in between the two substances, some light is reflected, some is absorbed and some is scattered and remaining can be transmitted.The opaque medium not transmits any light, so it only reflects, scatters and absorb all of the light incident on the surface. Opaque medium properties majorly depends upon the frequency of light also. so opaque medium do not allow any light to pass from them.

When and where opaque medium is used:

Opaque surface can be mostly used in home applications such as windows, doors, roof and wall systems.Opaque mediums are generally refers to common material which are neither metallic nor transparent too. Platic, wood, stone, ceramics are all acts as opaque mediums

Diffuse surface

Diffuse surfaces are the surface which provides the diffuse reflection. Diffuse reflection is known as the reflection of light in which any ray incident on the surface is scattered at many angle which are not parallel to each others. Ideal diffuse surface gives equal illumination. In diffuse surface, each point on the surface is on the different levels. It have various protrutions and throughs. Light once reflected from diffuse surface is not parallel but always at an angle

When and where diffuse surface is used:

Diffuse surface is used to determine the absorbtion spectra of the powered sample. When the transmission spectroscopy is not feasible, diffusion surfaces are used.

(b)

Emissive power

For any surface, emissivity can be defined as the effectiveness with which the surface can emit the energy in form of radiation. Radiation include both thermal as well as infrared radiation. Emmisivity of any surface can also be defined as the ratio of thermal radiation of the surface to the radiation from the the ideal black surface. Temperature is same in both the conditions. It can be given by stephan boltzman law and varies from 0 to 1.

Types of emissivity can be given as

• Hemispherical emissivity
• Spectral hemispherical emissivity
• Directional emissivity
• Spectral directional emissivity

Irradiation:

Irradiation is knowm as the process by which any object is exposed to the radiation. The irradiation can be generated from any source sometimes it can be natural source too. In general term irradiation can be defined as the total radiation incident on the surface. After falling on the surface some radiation can be absorbed reflected and transmitted.

Radiosity

Surfaces emits radiation and also reflects it. So in general when the radiation leaves the surface it have two components as emitted component of radiation and reflected component of radiation. So we need to define a quantity such that it represents the rate at which the radiation energy leaves the surface per unit area in all the directions.This term is called as radiosity and represented by J.

Absorptivity

Whenever there is radiation and it strikes the surface, there is some part is absorbed, some is reflected and in case iof remaining part of radiation if any, will be transmitted.

The fraction of the irradiation, which is absorbed by the surface is called absorptivity and it is represented by

Reflectivity

The fraction of the irradiation, which is reflected by the surface is called reflectivity. Reflectivity is denoted by

Transmissivity

The fraction of the irradiation, which is tramsmitted by the surface is called transmmitivity and denoted by