Magic Behind the Radiation-Quantum Theory of Radiation and Black body

On November 29

Magic Behind the Radiation-Quantum Theory of Radiation and Black body

Max Planck 1858 – 1947




     Max Planck, a German physicist, is the founder of quantum theory, and one of the most important  physicists . Planck important  his role as originator of the quantum theory. the observation that the greatest amount of energy being radiated from a “black body”


       One photon of light carries exactly one quantum of energy. Planck is considered the father of the Quantum Theory. According to Planck: E=h , where h is Planck's constant (6.62606957(29) x 10 -34 J s), ν is the frequency, and E is energy of an electromagnetic wave.


Quantum theory


         Max plank initiated Quantum physics according to which Energy is not emitted or absorbed, Its is emitted or absorbed in the form of wave packet or quanta . This quantum of light is called photon.


       E = m c2 The amount of energy associated with quantum of radiation is directly proportional to the frequency (v)   of radiation i. e, h=Planks Constant =6.626*10-34J.s

A body can emit or absorb energy only in term of integral multiple of a quantum/photon where n=1, 2, 3





 Planck’s Quantum Theory



         Comparison   between  Planck’ quantum theory and classical theory of energy.

Planck’s Quantum Theory Classical theory Energy of the e. m. f radiation is quantized.. Energy of e. m. f radiation depends on its frequency or wavelength Energy of e. m .f .radiation does not depend on its frequency or wavelength.



 Planck’s Quantum Theory

         The   Planck’s quantum theory is a theory of black body radiation. Black body is defined as an ideal system or object that absorbs and emits all the   e. m. f radiations that is incident on it. The electromagnetic radiation emitted by the black body is called black body radiation. An ideal black body, incident light is completely absorbed. Light that enters the cavity through the small hole is reflected multiple times from the is completely   absorbed.


        PHOTONS-   The quanta of light  , all electromagnetic radiation is quantized and in finite "bundles" of energy which we call photons. The quantum of energy for a photon is not Planck's constant h   but  the product of h and the frequency(v).



Planck  theory  are   : The   e .m. f radiation emitted by the black body is a discrete (separate) packets of energy known as quanta. This means the energy of e. m. f. radiation is   quantized . The energy size of the radiation depends on its frequency




        The equation E = m c2 implies that it is possible to convert mass into energy. One example of the conversion of energy to mass is pair production. A high ­energy photon known as a gamma ray traveling near the nucleus of an atom may disappear and an electron and  may appear in its place.  

    The electron and the positron have the same mass and carry the same magnitude of electric charge; however, the electron is negatively charged and the positron is positively charged.

    The minimum energy of a gamma ray required for the pair production of electron and positron is about 1.02 Me V If the energy of the gamma ray is above this amount, then  excess energy is shared equally between the particles in the form of kinetic energy.

At certain discrete temperature levels (exact multiples of a basic minimum value), energy from a glowing body will occupy different areas of the color spectrum.

Plank assumed that the emission and absorption of radiation always takes place in discrete portions of energy or energy quanta h ν, where ν is the frequency of absorbed or emitted radiation. Starting with this assumption, Planck arrived at his famous formula for the density of Black body radiation at temperature T.



Planck’s Quantum Hypothesis; Blackbody Radiation

blackbody  radiation curves for three different temperatures. Note that frequency increases to the left .The frequency of peak intensity increases linearly with temperature.


Planck’s Quantum Hypothesis; Blackbody Radiation

The energy of atomic oscillations within atoms cannot have an arbitrary value; it is related to the frequency: The constant h is now called Planck’s constant.


Planck’s Quantum Hypothesis; Blackbody Radiation

Planck found the value of his constant by fitting blackbody curves: Planck’s proposal was that the energy of an oscillation had to be an integral multiple of hf. This is called the quantization of energy.


Photon Theory of Light and the Photoelectric Effect

Einstein suggested that, given the success of Planck’s theory, light must be emitted in small energy packets: These tiny packets, or particles, are called photons

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