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(a) Show explicitly where the factor of 1/2 in parentheses in eq. (5.48) comes from in converting the classical expression in (5.46) to its quantum mechanical analog. (b) Eq. (5.48) may be rewritten as Arad = Ek,a Awk Nka + Ek,a 2 hok What does this say about the energy associated with the field when the number of photons is zero? Is this a problem? Head -= Ex Ea hok (akaaka + akaaka) Eq. 5.46 Ared - Ex Ea Awk ( at axa + 2) = Ex Ea hok ( Nka + ) Eq. 5.48