Introduction to Blackbody radiation spectrum Video Lecture | Physics for EmSAT Achieve

perfect black body and its spectrum a
perfect black body is one which absorbs
completely the radiations of all
wavelengths falling on it hence a
perfectly black body neither reflects
nor transmits any radiation it is for
the same reason that it appears black
irrespective of the wavelength of
incident radiation when a perfectly
black body is heated to a suitable high
temperature it emits radiations of all
possible wavelengths this radiation is
called blackbody radiation it is not
possible to attain a perfectly black
body a surface coated with lampblack or
platinum black is an example of a
perfect black body such a surface
absorbs 96% to 98% of the incident
radiation for accurate experiment work
the black body designed by fairy is
generally used fairies black body is a
closed double walled hollow sphere
having a small opening oh and a conical
projection P opposite to the opening the
projection prevents direct reflection of
any radiation it is painted black from
inside radiation entering the opening
suffers multiple reflections at the
inner walls after a few reflections
almost the entire radiation gets
absorbed when the body is heated it
becomes a source of thermal radiation
the radiation from a constant
temperature enclosure depends only on
the temperature of the enclosure it does
not depend on the nature of the
substance note radiation falling on the
hole is completely absorbed when the
sphere is heated blackbody radiation
emerges from the hole so it is the hole
which is to be regarded as a black body
and not the total enclosure
distribution of energy in the spectrum
of a blackbody in 1899 Lama and priam
experimentally studied the distribution
of energy in the spectrum of blackbody
radiation at different temperatures an
electrically heated enclosure with a
hole was used as a source of blackbody
radiation the radiation was passed
through a slit s and made to fall on a
concave reflector c1 the radiation was
then made to fall on a rock salt or
fluoride or fluorspar prison the prison
was placed on the turntable of a
spectrometer it was found that like
ordinary light the thermal radiation got
dispersed into its component wavelengths
when passed through fluorspar prism lama
and prince i'm use concave reflector to
focus the radiations on a sensitive
thermometer or below meter they
connected a galvanometer G in series
with a below meter the deflection of the
galvanometer gave the intensity of
radiation incident on the below meter
lama and printing measured the intensity
of radiation corresponding to different
wavelengths heating the body to
different temperatures they made a
number of observations the results of
the experiment were plotted graphically
as shown here each curve represents the
variation of monochromatic
immittance a gamma with wavelength
lambda let us now analyze the spectrum
we observe that no curve enters the
Whizzer bull region this is due to the
fact that the fluorspar prism absorbs
the radiation corresponding to the
wavelengths of the visible region the
distribution of energy among the
different wavelengths of the spectrum of
blackbody radiation is not uniform
at a given temperature the energy
initially increases with wavelength
becomes maximum corresponding to a
particular valent lambda m and then it
begins to decrease with an increase in
the temperature of the blackbody the
Maxima of the curves shift towards
shorter wavelengths in other words
lambda M decreases with an increase in
temperature
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