UtsavKishoreOjha_12500123180.pptx

BLACKBODY
RADIATION
 Name : Utsav Kishore Ojha
 College Roll No. : 232179342
 University Roll No. : 12500123180
 Subject : Basic Physics
 Stream : Computer Science Engineering
 Section : C

Contents of the slide
Introduction
Theory
Conclusion
Reference

INTRODUCTION
Blackbody radiationrefers to the electromagnetic radiation
emitted by a perfect absorber and emitter of energy,known as a
blackbody. A blackbody absorbs all incident radiationregardless of
frequency or angle, and it also radiates energy based solely on its
temperature.This phenomenonis described by Planck's law, which
introduced the concept of quantized energy levels and played a
crucial role in the developmentof quantum theory. Blackbody
radiationprovides a theoretical foundation for understandingthe
spectral distributionof emitted radiation at different temperatures,
forming the basis for diverse applicationsin physics and
astrophysics.

Stefan's Law
It is formulated by Austrian physicist Josef Stefan in 1879, relates the
total energy radiated by a blackbody per unit surface area to its
temperature. The law is expressed mathematically as:
E = σT⁴
where:-
• E is the radiant exitance (in watts per square meter)
• σ is the Stefan-Boltzmannconstant (5.670374419 × 10^-8 W⋅m⁻²⋅K⁻⁴)
• T is the absolute temperature of the blackbody (in kelvins)
Stefan's Law demonstrates that the total power radiated by a
blackbody is proportional to the fourth power of its temperature. This
law is fundamental in understanding how the intensity of emitted
radiation increases with temperature, playing a key role in various
areas of physics, astrophysics, and engineering.

Wien's Displacement Law
This law also focuses on blackbody radiation, but it sheds light on a different aspect: the
peak wavelength of the emitted radiation.
Here's the gist of Wien's law:
Hotter objects emit radiation at shorter wavelengths. Imagine a glowing ember in a fireplace.
As the temperature rises, the red glow intensifies and gradually shifts towards orange and
yellow, indicating shorter wavelengths . The product of an object's absolute temperature (in
Kelvin) and the peak wavelength of its emitted radiation remains constant. This constant
value, known as Wien's displacement constant (b), is approximately 2.898 x 10^-3 meter-
kelvin.
Here's the mathematical formula for Wien's law :
λ_max * T = b
where:
• λ_max is the peak wavelength of the emitted radiation (in meters)
• T is the absolute temperature of the blackbody (in kelvins)
• b is Wien's displacement constant
Think of it this way: As the temperature increases, the "bump" in the blackbody radiation
curve shifts towards shorter wavelengths, just like how a child on a seesaw moves closer to
the fulcrum as they get heavier. The product of their distance and weight always remains the
same.

Planck's Law
Unveiling the nature of light Planck's law formulated by the legendary physicist Max Planck in 1900,
delves deeper into the realm of blackbody radiation than its counterparts, Stefan's and Wien's laws. It
unveils the spectral distribution of the emitted radiation, meaning how the intensity of light varies
across different wavelengths.
Here's the essence of Planck's law :
Energy is quantized: Unlike classical physics, where energy can flow continuously like water from a
tap, Planck proposed that energy is emitted and absorbed in discrete packets called quanta. Think of it
like pearls on a necklace; you can't have half a pearl.
Energy of quanta depends on wavelength: Each quantum of light, also known as a photon, carries an
energy directly proportional to its frequency (and inversely proportional to its wavelength). Higher
frequencies (shorter wavelengths) correspond to higher energy photons . Spectral intensity varies
with wavelength: Planck's law mathematically describes the relationship between the intensity of
emitted radiation and its wavelength at a specific temperature. The intensity peaks at a particular
wavelength and then falls off gradually on either side.
Implications of planks law:-
 Birth of quantum mechanics:-Planck's law marked a revolutionary shift from
classical physics to quantum mechanics, where energy comes in discrete packets
and waves have particle-like properties.
 Understanding stellar colors:-By analyzing the spectrum of light from stars,
astronomers can estimate their temperatures and stages of evolution.
 Developing energy technologies:- Planck's law plays a crucial role in
designing efficient solar cells, LEDs, and other light-emitting.

Rayleigh-Jeans Law
The Rayleigh-Jeans law, formulated by Lord Rayleigh in 1900 and subsequently refined by James
Jeans, was a valiant attempt to explain the spectral distribution of blackbody radiation using the
principles of classical physics. While ultimately found to be incomplete, it played a crucial role in
the development of quantum mechanics.
Here's the essence of the law :
Classical approach: Unlike Planck's law, which embraces the quantum nature of light, Rayleigh-
Jeans law relies on the equipartition theorem from classical mechanics. This theorem states that
in thermal equilibrium, the average energy of each degree of freedom of a vibrating system is equal
to kT/2, where k is Boltzmann's constant and T is thetemperature .
Energy density proportional to frequency squared: Based on this principle, Rayleigh and Jeans
envisioned blackbody radiation as a collection of harmonic oscillators (think of vibrating strings)
with different frequencies. Each oscillator would contribute an energy proportional to its
frequency squared. Intensity peaks at short wavelengths: Consequently, the law predicted that the
intensity of emitted radiation would increase rapidly with increasing frequency and peak at very
short wavelengths (ultraviolet and beyond).
Significance of Rayleigh-Jeans Law :
Despite its shortcomings, the Rayleigh-Jeans law played a pivotal role in
the development of quantum mechanics. Its failure to explain the observed
spectrum of blackbody radiation prompted Max Planck to propose his
revolutionary quantum theory of light, laying the foundation for a new
understanding of the microscopic world.

The Ultraviolet Catastrophe
It refers to a problem in classical physics related to the predicted
behaviorof blackbody radiation. According to classical physics,as the
frequency of radiationincreases, the energy emitted should become
infinite, leading to a catastrophic divergence. This issue was resolved
with the developmentof quantum theory, particularly Max Planck's
introduction of quantized energy levels, which explained the observed
spectrum without the catastrophic divergence.

CONCLUSION
Blackbody radiationis a fundamental concept in physics that
describes the emissionand absorptionof electromagneticradiation
by a perfect absorber and emitter of energy. Key laws governing
blackbody radiation include Stefan's Law, which relates the total
power radiated to temperature,and Wien's Law, which connects the
peak wavelength to temperature. Planck's Law, developedto
address the shortcomingsof earlier models, is a cornerstone of
quantum theory, providing an accurate description of the spectral
distributionof blackbody radiation. Understandingthese principles
is crucial for various applications in physics, astrophysics,and
engineering,making blackbody radiationa fundamentaland
fascinating topic in the realm of electromagneticphenomena.

REFERENCE
For a comprehensive and authoritative reference on
blackbody radiation, we may consider using a reputable
physics textbook or academic source. "Introduction to
Electrodynamics" by David J. Griffiths, "Modern Physics" by
Paul A. Tipler and Ralph Llewellyn, or "Principles of Physics"
by Resnick, Halliday, and Walker are excellent choices.
Additionally , scientific papers or online resources from
reputable sources like the American Physical Society (APS),
Institute of Physics (IOP), or educational institutions such as
MIT Open Course Ware can provide more in-depth
information and references for our presentation.

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