If the length of a conduction path is doubled, what happens to the thermal resistance?

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Multiple Choice

If the length of a conduction path is doubled, what happens to the thermal resistance?

Explanation:
In conduction, how hard it is for heat to flow (the thermal resistance) grows directly with the distance the heat has to travel. For a simple, uniform material, the thermal resistance is R_th = L / (kA), where L is the path length, k is the material’s thermal conductivity, and A is the cross-sectional area. If you double the length while keeping k and A the same, the resistance becomes R_th' = 2L / (kA) = 2 R_th. So the thermal resistance increases by a factor of two. This also means that, for the same temperature difference, the heat transfer rate would drop by half.

In conduction, how hard it is for heat to flow (the thermal resistance) grows directly with the distance the heat has to travel. For a simple, uniform material, the thermal resistance is R_th = L / (kA), where L is the path length, k is the material’s thermal conductivity, and A is the cross-sectional area. If you double the length while keeping k and A the same, the resistance becomes R_th' = 2L / (kA) = 2 R_th. So the thermal resistance increases by a factor of two. This also means that, for the same temperature difference, the heat transfer rate would drop by half.

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