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Planck’s Law UPSC NOTE

 What is Planck’s Law

  • Planck's law, also known as Planck's radiation law.

  • It describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature.

  • Spectral density: This refers to the amount of energy emitted per unit wavelength range.

  • Black body: This is a hypothetical object that absorbs all electromagnetic radiation falling on it and emits radiation based solely on its temperature. 

  • It's a theoretical concept, but it acts as a useful idealization for real objects.

  • Thermal equilibrium: This means the object has reached a constant temperature without exchanging heat with its surroundings.

  • Before Planck came along, the existing theories couldn't explain the observed spectrum of black-body radiation accurately, especially at higher frequencies. In 1900.

  • Energy is not emitted continuously but in discrete packets called quanta

  • These packets are named after Planck's constant, a fundamental physical constant.

  • The energy of each quantum is proportional to its frequency. 

  • This means higher-frequency radiation (like blue light) carries more energy per quantum than lower-frequency radiation (like red light).

Bose’s derivation

  • Bose's derivation, published in 1924, aimed to explain the black-body radiation spectrum using a novel statistical approach. 

  • This approach differed from classical statistical mechanics and introduced a new counting of states for indistinguishable particles:

  • Classical mechanics: Assumed particles are distinguishable, leading to an overestimation of high-energy states

  • Bose's approach: Recognized that identical particles like photons could occupy the same energy state, effectively "grouping" them in these states. 

  • This led to a lower probability of high-energy states, resolving the "ultraviolet catastrophe" issue.

Satyendra Nath Bose – Best known for?

  • Satyendra Nath Bose appeared on the physics scene like a comet.

  • The year was 1924. 

  • Physics was in the middle of the biggest upheaval in its history. 

  • The old foundations had crumbled in the face of new data. 

  • The picture of a new ‘quantum theory’ was emerging

  • But it was a fractured, disjointed picture with major pieces missing.

  • The search was on among physicists to find the pieces and complete the jigsaw

  • In the best universities of Europe, new ideas were being proposed, debated, and discarded every week. 

  • Then a lecturer of physics from Dhaka University — located then in the backwater of backwaters — appeared out of nowhere with a major missing piece of the puzzle.

  • The lecturer, Satyendra Nath Bose, had discovered the correct set of equations to use to work out the behaviour of collections of photons (particles of light). 

  • As physics work goes, Bose’s was as fundamental as it got. 

  • The physicist and writer Abraham Pais listed it as one of the six foundational papers of quantum theory. 

  • Even so, a paper from an unknown Indian scientist was initially rejected by a journal

  • Bose then mailed the paper to his favourite physicist, Albert Einstein, hoping to secure the giant’s support. 

  • Einstein loved the paper, translated it to German, and sent it to a journal himself.

  • This year marks 100 years of Bose’s discovery.



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Planck’s Law UPSC NOTE
Planck’s Law UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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