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)
2 k₁ k₂/ (k₁ + k₂)
(k₁ + k₂)/ k₁ k₂

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Heat and Mass Transfer
Kirchhoff's law states that

None of these
The wave length corresponding to the maximum energy is proportional to the absolute temperature
The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body

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Heat and Mass Transfer
Conduction is a process of heat transfer

From one particle of the body to another without the actual motion of the particles
None of these
From one particle of the body to another by the actual motion of the heated particles
From a hot body to a cold body, in a straight line, without affecting the intervening medium

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