The document discusses electromagnetic radiation and heat transfer. It defines key terms like blackbody, opaque body, and gray body. The electromagnetic spectrum is described along with examples of different types of radiation. Factors that influence radiation emission like temperature and surface properties are outlined. Equations are provided for total emissive power and monochromatic emissive power. Absorptivity, reflectivity, and transmissivity are defined in relation to the conservation of energy principle.

2. :-
DEFINITION OF RADIATION
SPECTRUM OF ELECTROMAGNETIC REDIATIONS.
SURFACE EMISSION PROPERTIES.
ABSORPTIVITY, REFLECTIVITY AND TRANSMISSIVITY
BLACK BODY
OPAQUE BODY
WHITE BODY
GRAY BODY

3. The transfer of energy across a system boundary
by means of an electromagnetic mechanism wich
is caused solely by a temperature difference.
Radiation heat transfer does not require a
medium.
The radiant heat exchange between two bodies
depends on the difference between their
temperature to the Fourth power.
E=σT4 W/m2
E=σAT4 watt

4. The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that
travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio
waves that come from a radio station are two types of electromagnetic radiation. The other types of EM
radiation that make up the electromagnetic spectrum are microwaves, infrared light, ultraviolet light, X-
rays and gamma-rays.
Radio: Your radio captures radio waves emitted by radio stations, bringing
your favorite tunes. Radio waves are also emitted by stars and gases in
space.
Microwave: Microwave radiation will cook your popcorn in just a few
minutes, but is also used by astronomers to learn about the structure of
nearby galaxies.
Infrared: Night vision goggles pick up the infrared light emitted by our skin
and objects with heat. In space, infrared light helps us map the dust between
stars.
Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit
visible light.
Ultraviolet: Ultraviolet radiation is emitted by the Sun and are the reason
skin tans and burns. "Hot" objects in space emit UV radiation as well.
X-ray: A dentist uses X-rays to image your teeth, and airport security uses
them to see through your bag. Hot gases in the Universe also emit X-rays.
Gamma ray: Doctors use gamma-ray imaging to see inside your body. The
biggest gamma-ray generator of all is the Universe.

5. The rate of emission of radiation by a body depends upon the following factors:-
A. Temperature of surface.
B. The nature of surface, and
C. the wavelength or frequency of radiation.
The parameters which deals with the surface emission propertiesare given below:-
1. Total emissive power:-Total amount of radiation emitted by a body per unit area and time.
Eb=σT4 W/m2
Eb=σAT4 watt σ=Stefan-Boltzmann Constant=5.67x10-8 w/m2K4
2. Monochromatic emissive power:- The rate of energy radiated per unit area of the surface
per unit wavelength.
3. Emission from real surface emissivity:- It can be calculated by.
Eb=ἐσAT4
ἐ=Emissivity of the material=Ability of the surface of a body to radiate heat.

6. Let,
G=Incident radiation
Gr=Reflected radiation
Gt=Transmitted radiation
Ga=Absorbed radiation
By the conservation of energy principle
Ga +Gt +Gr =G
Dividing both sides by G, We get
ABSORBED RADIATIONS

7. Blackbody is an idealized physical body that absorbs all incident
electromagnetic radiation, regardless of frequency or angle of
incidence.
For a black body, τ = 0, α = 1, and ρ = 0.
Planck offers a theoretical model for perfectly black bodies,
which he noted do not exist in nature: besides their opaque interior,
They have interfaces that are perfectly transmitting and non-reflective.

8. When no incident radiarions is
transmitted through the body, It is
called an “Opaque Body”
That is, τ = 0 and α + ρ = 1.
ABSORBED RADIATIONS

9. If all the incident radiation falling
on the body are reflected , It is
called “White Body”.
That is, τ = 1 and α = ρ = 0.
Type of reflection
1. Regular reflection
2. diffuse reflection

10. A grey body is defined as a body
with constant emissivity over all
wavelengths and temperatures.
or
A grey body is one where α, ρ and
τ are constant for all wavelengths.