A plane wall of thickness L is subjected to convection at both surfaces with ambient temperature T_∞1 and heat transfer coefficient h₁ at inner surface, and corresponding T_∞2 and h₂ values at the outer surface. Taking the positive direction of x to be from the inner surface to the outer surface, the correct expression for the convection boundary condition is

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(a) k =h₁[T(0) Tl)] =h₂[T(L) - To2)] (c) -k- = h₁ [Tool - T₂)] dT(0) dx dT(0) dx dT (L) dx (b) k dT (L) dx (e) None of them (d) -k- =h₂[Tx1 - Tx₂)]