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# When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

α = 1, ρ = 0 and τ = 0

α = 0, ρ = 1 and τ = 0

α = 0, ρ = 0 and τ = 1

α + ρ = 1 and τ = 0

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