Physics

Physics

Problem

A copper rod is to remove 100 W100\,\text{W} of heat steadily from a hot surface at 120 ∘C120\,^{\circ}\text{C} to a sink at 30 ∘C30\,^{\circ}\text{C}. The rod is 0.20 m0.20\,\text{m} long and the thermal conductivity of copper is 400 W m−1 K−1400\,\text{W m}^{-1}\,\text{K}^{-1}. The minimum cross-sectional area needed is a) 4.2×10−4 m24.2\times10^{-4}\,\text{m}^2 b) 1.1×10−3 m21.1\times10^{-3}\,\text{m}^2 c) 5.6×10−4 m25.6\times10^{-4}\,\text{m}^2 d) 5.6×10−5 m25.6\times10^{-5}\,\text{m}^2

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