Four identical rods and have the same length and cross-sectional area

PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

Four identical rods P,  Q,  RP,\;Q,\;R and SS have the same length and cross-sectional area. Their materials and thermal conductivities are: PP: copper (400 W m−1 K−1)(400\,\text{W}\,\text{m}^{-1}\,\text{K}^{-1}), QQ: aluminium (205 W m−1 K−1)(205\,\text{W}\,\text{m}^{-1}\,\text{K}^{-1}), RR: glass (1.0 W m−1 K−1)(1.0\,\text{W}\,\text{m}^{-1}\,\text{K}^{-1}), SS: hard rubber (0.15 W m−1 K−1)(0.15\,\text{W}\,\text{m}^{-1}\,\text{K}^{-1}). The ends of every rod are kept at 100 ∘C100\,^{\circ}\text{C} and 20 ∘C20\,^{\circ}\text{C} respectively and steady-state heat conduction is allowed to set in. (i) Arrange the rods in descending order of the rate of heat flow through them. (ii) Justify your answer without performing any numerical calculation. (iii) Which one of the above materials is most suitable for making the handle of a cooking utensil? Give reasons based on thermal conductivity.

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