Heat and Mass Transfer
A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

(k₁ + k₂)/ k₁ k₂
(k₁ + k₂)
2 k₁ k₂/ (k₁ + k₂)
k₁ k₂

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Heat and Mass Transfer
According of Kirchhoff's law

Emissive power depends on temperature
Emissive power and absorptivity are constant for all bodies
Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body
Radiant heat is proportional to fourth power of absolute temperature

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