Heat Transfer
List of Important Definitions &
Points :
1) Heat Transfer – It is the process by which
heat is transferred from one part of a
system / body to another part of the same
body or from one system to another
system arising due to the temperature
difference between the two parts of the
same body or the two systems.
2) Conduction – It is the mechanism of heat
transfer between the adjacent parts of the
same body due to the temperature
difference between the two parts without
the actual movement of particles from
there equilibrium positions.
3) Convection – It is the process by which
heat is transferred from one system to
another due to temperature difference
between two parts by the actual movement
of material particles from a region pf higher
temperature to a region of lower
temperature.
, 4) Radiation – The process by which energy is
emitted from a body in the form of
radiation, by virtue of it’s temperature is
called radiation. The energy radiated from
a body is called radiant energy and this
radiant energy is emitted by all bodies
above absolute zero.
Properties of Thermal Radiation :
a.Thermal radiation belongs to the
electromagnetic spectrum i.e., ultraviolet
radiation, X-Rays, infra red radiation,
microwaves and visible light.
b.It can pass through vacuum and other
transparent media. Its velocity is same as
that of light (3 × 10^8 m/s).
c. It exhibits the properties of reflection,
refraction, diffraction, interference and
polarisation.
d.The wavelength of thermal radiation is
longer than that of visible light i.e, the
wavelength of thermal radiation is of the
range ((8×10^-7)m to (3×10^-4)m) ,
while the wavelength of visible light is of
the range ((4×10^-7)m to (8×10^-7)m).
5) Derivation of formulas of Absorptance,
Reflectance and Transmittance :
Let us consider an amount of energy ‘Q’
incident on a surface, out of which an
amount ‘Q1’ is absorbed by the surface, an
List of Important Definitions &
Points :
1) Heat Transfer – It is the process by which
heat is transferred from one part of a
system / body to another part of the same
body or from one system to another
system arising due to the temperature
difference between the two parts of the
same body or the two systems.
2) Conduction – It is the mechanism of heat
transfer between the adjacent parts of the
same body due to the temperature
difference between the two parts without
the actual movement of particles from
there equilibrium positions.
3) Convection – It is the process by which
heat is transferred from one system to
another due to temperature difference
between two parts by the actual movement
of material particles from a region pf higher
temperature to a region of lower
temperature.
, 4) Radiation – The process by which energy is
emitted from a body in the form of
radiation, by virtue of it’s temperature is
called radiation. The energy radiated from
a body is called radiant energy and this
radiant energy is emitted by all bodies
above absolute zero.
Properties of Thermal Radiation :
a.Thermal radiation belongs to the
electromagnetic spectrum i.e., ultraviolet
radiation, X-Rays, infra red radiation,
microwaves and visible light.
b.It can pass through vacuum and other
transparent media. Its velocity is same as
that of light (3 × 10^8 m/s).
c. It exhibits the properties of reflection,
refraction, diffraction, interference and
polarisation.
d.The wavelength of thermal radiation is
longer than that of visible light i.e, the
wavelength of thermal radiation is of the
range ((8×10^-7)m to (3×10^-4)m) ,
while the wavelength of visible light is of
the range ((4×10^-7)m to (8×10^-7)m).
5) Derivation of formulas of Absorptance,
Reflectance and Transmittance :
Let us consider an amount of energy ‘Q’
incident on a surface, out of which an
amount ‘Q1’ is absorbed by the surface, an
