This presentation is dedicated to students who has this topic as their slide presentation

1. BLACKBODY RADIATION AND
STORY OF STARS
By: SAMIM SK
ROLL NO – 2116223-180109, REG NO
058656 OF 2018-2019

2. DEFINATION OF
BLACKBODY
A black body is an ideal body which allows the
whole of the incident radiation to pass into itself
( without reflecting the energy ) and absorbs
within itself this whole incident radiation
(without passing on the energy). Is called a
Blackbody.

3. EXAMPLES OF
BLACKBODY
•INCANDESCENT BULB
• HOT LAVA
• SUN AND STARS
•HEATED METAL
• HOT METSL
• QUICKLY HEATED ICECUBES.

4. IMOPRTAN
CE
•The black body notion is important in studying
thermal radiation and electromagnetic
radiation energy transfer in all wavelength
bands.
• Black body as an ideal radiation absorber and
it is used as a standard for comparison with the
radiation of real physical bodies
•BLACK BODY RADIATIION IS USED HIGHLY IN THE
FIELD OF ASTRONOMY TO CALCULATE STARS
TEMPERATURE SIZE COLOR AND LUMINOCITY

5.  The blackbody radiation of stars or any blackbody produces a continuous
spectrum, classical mechanics failed to explain this.
 A graph of intensity against wavelength for blackbody radiation is known as
blackbody curve which depends upon temperature. The graph is given below

6. LAWS OF BLACK BODY RADIATION
•
•The Rayleigh-Jeans Law
•Planck’s Law
•Stefan Boltzmann Law
•Wein Displacement

7. Black-Body
Radiation laws (1)
The Rayleigh-Jeans Law
It agrees with experimental
measurements for long wavelengths.
It predicts an energy output that
diverges towards infinity as
wavelengths grow smaller.
The failure has become known as
the ultraviolet catastrophe.

8. BLACK-BODY
RADIATION LAWS (2)
The Planck Law gives a distribution that peaks at a certain
wavelength, the peak shifts to shorter wavelengths for higher
temperatures, and the area under the curve grows rapidly with
increasing temperature. Planck first explained the blackboy
radiation curve with his law and quantum view point.
Planck’s Law

9. Equations of
Planck's law
We have two forms, As a function of
frequency ,
As a function of wavelength,

10. BLACKBODY
RADIATION LAW
(3)
The Stefan-Boltzmann Law
The thermal energy radiated by a blackbody radiator per second per unit
area is proportional to the fourth power of the absolute temperature and is
given by,
Gives the total energy being emitted at all wavelengths by the
blackbody
Explains the growth in the height of the curve as the
temperature increases
Sigma = 5.67 * 10-8 J s-1 m-2 K-4 , Known as the Stefan
Boltzmann constant

11. BLACK-BODY
RADIATION LAWS (4)
Wien Displacement Law
It tells us as we heat an object up, its color changes from red to
orange to white hot.
You can use this to calculate the temperature of stars
The surface temperature of the Sun is 5778 K, this temperature
corresponds to a peak emission = 502 nm = about 5000 Å.
The surface temperature of the
Sun is 5778 K, this temperature
corresponds to a peak emission =
502 nm = about 5000 Å

12. Color of stars wiens law
•Hotter objects emit most of their radiation at shorter
wavelengths, hence they will appear to be bluer
• Cooler stars emit most of their radiation at longer wavelengths,
hence they will appear to be redder.
•at any wavelength, a hotter object radiates more (is more
luminous) than a cooler one
The effective temperature of the Sun is 5778 K.
Using Wien's law, Using Wien's law, this
temperature corresponds to a peak emission at
a wavelength of 2898um0k / 5778 K = 502 nm =
about 5000 Å.

14. Colors of star
The hottest stars have temperatures of over 40,000 K, and the coolest stars have temperatures of
about 2000 K. Our Sun’s surface temperature is about 5778 K its peak wavelength color is a slightly
greenish-yellow. In space, the Sun would look white, It looks somewhat yellow as seen from Earth’s
surface because our planet’s nitrogen molecules.

15. Temperature of stars
Stars as blackbodies show their visibility color depends upon the temperature of
the radiator. The curves show blue, white, and red stars. The white star is
adjusted to 5270K so that the peak of its blackbody curve is at the peak
wavelength of the sun, 550 nm. From the wavelength at the peak, the
temperature can be deduced
From the Wien displacement law we get the product of the peak wavelength
and the temperature is found to be a constant. And its value is 2898 x 10-3 m
K

16. Size of stars
Size of stars can be calculated using Stefan-Boltzmann Law.
(the intrinsic brightness of star is called luminosity)
Making T larger makes each square meter of
the star brighter
Making R larger increases the number of
square meters
If the luminosity (L) and temperature (T) are known, the size (R)
of a star can be deduced.