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I am a beginner and I have a problem regarding Planck's Quantum Theory

The following is one of the postulate of Planck's Quantum Theory

1) The energy of each quantum is directly proportional to frequency of radiation.

Q.) What is the sense of the word "frequency" here, despite the fact that Planck's Quantum theory contradicts wave nature of Electromagnetic radiations? (Since, Frequency is defined for waves).

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marked as duplicate by Thomas Fritsch, Jon Custer, PM 2Ring, John Rennie energy Jun 15 at 9:50

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Planck's theory does not contradict the wave theory. EM waves, including visible light, have wavelengths and frequencies which can be measured by various appropriate techniques and are related by $c=f \lambda$. They have energy - Poynting vector and all that. Planck said (reluctantly!) that the energy in a particular EM wave is not arbitrary but has to be an integer number of the quantum energy $hf$.

It's like going to a shop: you can't buy 123.4 grams of sugar. It comes in packets of 500g. You can get 500 or 1000 or 1,500... grams. Light with a wavelength of, say, 500 nm comes in packets of 2.48 eV so you can get 2.48 or 4.96 or 7.44... eV. But the light in a 2.48 eV quantum is still 500 nm light, just as the sugar in a 500g packet of sugar is still sugar.

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