# A doubt regarding Planck's quantum theory [duplicate]

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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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 $$hf$$.