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Each has an energy related to the frequency of the wave given by Planck 's relation " E = hf " , where " E " is the energy of the photon , " h " is Planck 's constant , 6.626 × 10 J · s , and " f " is the frequency of the wave .
 Planck, Planck
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Planck, Planck