PLAN'S THEORY Stefan’s Law, Wien’s displacement law Bhor's Model and its limitations PHOTO ELECTRIC EFFECT COMPTON EFFECT

2. Contents

3. introduction
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.
Its characteristics are sometimes are used in describing
and studying artificial electromagnetic radiation (in radio
and TV- broadcasting and communication).

4. Definition of black body
An ideal body which absorbs all the electromagnetic
radiation that strikes it so that all incident radiation is
completely absorbed.

5. Concept of black body
Why black body??
Because those bodies that absorb incident visible light well seem
black to the human eye.
Example: We can hardly characterize our sun which is indeed
almost a black body within a very wide band of electromagnetic
radiation wavelength as a black physical object in optics. It is namely
bright-white sunlight which represents the equilibrium black body
radiation.

6. Concept of black body
Application :
Optical band (surfaces approach an ideal black body in their
ability to absorb radiation) such as soot, silicon carbide,
platinum and golden niellos.
Earth surfaces (water surfaces, ice, land) absorb infrared
radiation well and in thermal IR band, these physical objects are
ideal black bodies.

7. Concept of black body

8. Concept of black body
Black body radiation /
Cavity radiation
The electromagnetic radiation that would be
radiated from an ideal black body

9.  A good approximation of a
black body is a small hole
leading to the inside of a
hollow object
 The hole acts as a perfect
absorber
 The nature of the radiation
leaving the cavity through
the hole depends only on
the temperature of the
cavity
Blackbody Approximation

10. Intensity of Blackbody Radiation,
Summary
• The intensity increases
with increasing
temperature
• The amount of radiation
emitted increases with
increasing temperature
– The area under the curve
• The peak wavelength
decreases with increasing
temperature

11. Energy spectrum
EM Radiation : A kind of radiation including visible light, radio
waves, gamma rays, and X-rays, in which electric and magnetic fields
vary simultaneously.
Energy spectrum based on the EM spectrum.
EM Spectrum : The distribution of electromagnetic radiation
according to energy (or equivalently, by virtue of the relations in the
previous section, according to frequency or wavelength).

14. Energy spectrum
Spectrum of Electromagnetic Radiation
Region Wavelength
(Angstroms)
Wavelength
(centimeters)
Frequency
(Hz)
Energy
(eV)
Radio > 109 > 10 < 3 x 109 < 10-5
Microwave 109 - 106 10 - 0.01 3 x 109 - 3 x 1012 10-5 - 0.01
Infrared 106 - 7000 0.01 - 7 x 10-5 3 x 1012 - 4.3 x 1014 0.01 - 2
Visible 7000 - 4000 7 x 10-5 - 4 x 10-5 4.3 x 1014 - 7.5 x 1014 2 - 3
Ultraviolet 4000 - 10 4 x 10-5 - 10-7 7.5 x 1014 - 3 x 1017 3 - 103
X-Rays 10 - 0.1 10-7 - 10-9 3 x 1017 - 3 x 1019 103 - 105
Gamma Rays < 0.1 < 10-9 > 3 x 1019 > 105

16. At a particular temperature the
distributed energy is not uniform
among the various wavelengths of the
radiation emitted by the black body.
For each temperature there is a
wave length (λm) at which energy
radiated is maximum (=Em ).
Increase in temperature Em
increases but the corresponding
(λm )decreases
The area under the curve for a
particular temperature gives the total
energy emitted by the black body per
unit area per second for the complete
spectrum .

17. Stefan’s law
Stefan’s Law or Stefan’s Boltzmann’s Law
The energy radiated by a blackbody radiator per second
per unit area is directly proportional to the fourth power of
the absolute temperature.

18. Stefan’s law
Stefan’s Law (1879, 1884)
 Josef Stefan deduced the rule in 1879 and Ludwig Boltzmann
provided a formal derivation in 1884.
 Classical physics
 Explain the growth in the height of the curve as the
temperature increase.
 Energy emitted increase rapidly with an increase in
temperature which is proportional to the temperature raised to the
fourth power.

19. Stefan’s law
Formula
Where
F= energy flux
T = Temperature
σ = Stefan Constant

20. wein’s displacement law
The black body radiation curve for
different temperature peaks at a wavelength
inversely proportional to the temperature.
Wein’s
Displacement Law,
1893

21. wein’s displacement law
Formula
Unit constant, c : meter per Kelvin (m/K)
λmax = c = 2.898x10-3
T T

22. Rayleigh-Jeans Law
 This law explains blackbody radiation
𝑬𝝀 =
𝟖𝝅𝑲𝑻
𝝀 𝟒
𝑩𝒐𝒍𝒕𝒛𝒎𝒂𝒏𝒏′ 𝒔𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕 = 𝟏. 𝟑𝟖𝟎𝟔𝑿𝟏𝟎−𝟐𝟑
• At long wavelengths, the law
matched experimental results
fairly well
• At short wavelengths, there
was a major disagreement
between the Rayleigh-Jeans
law and experiment

23. clasical theory
This theory stats that
“Black body radiation whose wavelength
and colour that depends on the temperature
of the object. The wavelength of energy
emitted by an object depends on only its
temperature, not its surface or
composition.”

24. Classical theory could not explain the sharp
decrease in the intensity of radiation emitted
at shorter wavelengths.
Limitation of classical theory

25. Max Planck
Introduced the concept of “quantum
of theory ”
In 1918 he was awarded the Nobel
Prize for the discovery of the quantized
nature of energy

26. Plank observed the Rayleigh-jeans and wein’s law
and developed theory.
According to this theory
Radiant energy is emitted or absorbed
discontinuously in the form of tiny bundles of energy
known as quanta. This can be expressed by
Where,
Max Planck theory

27. A body can emit or absorb energy only in whole number
multiplies of quantum number i.e 𝟏𝒉𝒗, 𝟐𝒉𝒗, 𝟑𝒉𝒗 … … … , 𝒏𝒉𝒗.
Energy in fraction of a quantum cannot be lost or absorbed.
This is known as quantization of energy.
Based on this theory plank obtained the following expression
for energy density of black body radiation
𝑬𝝀 =
𝟖𝝅𝒉𝒄
𝝀 𝟓
×
𝟏
𝐞𝐱𝐩(
𝐡𝐜
𝐊𝐓𝛌
) − 𝟏
Where,
(h)= Planck’s constant, the
(c)= speed of light
(k)= Boltzmann constant and
(T)=absolute temperature
Max Planck theory

28. Photo electric effect
Photo electric effect is a process in which electrons
are emitted when radiation of a certain frequency
strikes the surface of a metal.
This was observed by Sir J.J Thomson in
some his experiments. The electrons that are
emitted are called photoelectrons.
It was found that the emission of electron from a
given metal depended on the frequency of the
radiation and not on the intensity. Thus for every
metal there exists a minimum frequency called the
threshold frequency . Only radiation equal to this
frequency or above it can cause emission of electron
from the surface of metal.

29. Photo electric effect
On the basis of quantum theory Einstein gave an expression
for the photo electric effect
ℎ𝜗 = Ф +
1
2
𝑚𝑣2
where
 Ф is threshold energy of the metal

1
2
𝑚𝑣2
is kinetic energy

30. electrons in orbits
nucleus
Bohr’s Atomic model

31. Postulates of Bohr’s Theory
1. In an atom, the electrons revolve around the nucleus in
certain definite circular paths called orbits, or shells.. Each
shell or orbit corresponds to a definite energy. Therefore,
these circular orbits are also known as energy levels or
energy shells.
2. The electrons revolve rapidly around the nucleus in fixed
circular paths called energy levels or shells. These can
represented by number 1,2,3,4,…or by letters K,L,M,N…..
3. When an electron jumps from a higher energy level to a
lower one, the amount of energy absorbed or emitted is
given by the difference of energies associated with the two
levels
The energy absorbed or lost is equal to the difference
between the energies of the two energy levels, i.e.,
ΔE= Ehigher - Elower

32.  Angular momentum of an electron moving
around the nucleus is quantised.
mvr = (
ℎ
2𝜋
)n
Where
m=mass
v= linear velocity of an electron and
r= radius of the electron.
Postulates of Bohr’s Theory

33. This model was applicable only for those
atoms which have one electron.
Bohr theory explained only spherical orbits.
This model failed to explain Zeeman Effect
and stark effect.
Bohr model could not explain the uncertainty
principle of Heisenberg.
Bohr model could not explain the wave nature
of electron. It explained only particle nature of
electron.
Limitations of Bohr’s Model

34. Arthur Compton found that. “If monochromatic X-
rays are allowed to fall on carbon or some other
lighter elements, the scattered X-rays have
wavelength larger than the incident rays. In other
words, the scattered X-rays have low frequency than
the incident rays. This causes decrease in the energy
of incident ray.
Compton effect

35. Compton effect
By applying law of conservation of energy and the law of
momentum and assuming X-rays to consist of photons, having
energy equal to ℎ𝜗 Compton shows that
∆λ = (
2ℎ
𝑚𝑐
)sin2
(
𝜃
2
)
Where, ∆λ = Compton shift
m = mass of the electron
C = velocity of light
𝜃 = angle between incident and scattered X-rays.

36. Reference
 Physical chemistry
(Puri Sharma)
Physical chemistry
(R.LMadan)
 phy sical chemistry
(a.s negi S.C anand)

37. ~ ~The end~ ~
“If you really want to do something, you will find
a way. If you don't, you will find an excuse.“
-JimRohn-