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Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K₁ and K₂. The thermal conductivity of the composite rod will be:

1. 3(K₁ + K₂)/2
2. K₁ + K₂
3. 2(K₁ + K₂)
4. (K₁ + K₂)/2

Correct answer: (K₁ + K₂)/2

Solution

When two rods of different materials are welded together in series, the effective thermal conductivity of the composite rod is the average of their individual conductivities. Hence, the thermal conductivity is (K₁ + K₂)/2.

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