https://foxoyo.com/mcq/95313/what-is-the-critical-radius-of-insulation-cms-for-a-metallic-cylinder-if-the-convective-heat-transfer-co-efficient-with-the-ambient-atmosphere-is-5-wm2-k-thermal-conductivity-of-metal-and-insulation-material-are-40-and-01-wmk-respectively