An iron bar and a brass bar, each of length L, are soldered end to end, in series, with each other. The free ends of the combined bar are maintained at different temperatures. What is the equivalent thermal conductivity of the compound bar K^', given that thermal conductivity of iron is K₁ and of brass is K₂ ?

K’ = 1/ K₁+ 1 / K₂

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K’ = K₁ + K₂

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Solution

The correct option is D

The length of the combined rod is 2L.

The thermal resistance of iron rod is R_iron = (1/K₁)(L/A)
The thermal resistance of brass rod is R_brass= (1/K₂)(L/A)

The equivalent thermal resistance is R = R_iron + R_brass

The thermal conductivity of the combined rod will be

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