Suitability of the saucepan and handle in terms of heat transfer. Calculation of heat gained by the water. How the thermos flask reduces heat transfer. Why gaps are provided in bridges and railway lines.

1. Conduction: The vacuum between the double glass walls is a poor conductor of heat, preventing heat transfer by conduction. The insulating stopper and base also reduce conduction.
2. Convection: The vacuum prevents the movement of air or water between the walls, thus stopping heat transfer by convection.
3. Radiation: The silvered (shiny) surfaces on the inner walls reflect infrared radiation back into the flask, minimizing heat loss by radiation. The narrow neck and insulating stopper further minimize heat transfer by conduction and convection.

d) Gaps are provided in bridges and railway lines to accommodate the thermal expansion of materials in hot weather and contraction in cold weather. Without these gaps, the expanding metal could buckle or bend, and in bridges, it could lead to cracking or damage to the structure, compromising safety and integrity.