Question

_______is a special bottle that is used to keep liquids hot for a long time.

Answer 1

1. A thermos flask is a double-walled glass bottle with a vacuum between the two walls.
2. As the glass is a bad conductor of heat and reduces the heat loss by conduction.
3. The vacuum reduces the heat loss by conduction and convection.
4. The inner side of both the walls is silver coated. Since shiny surfaces are good reflectors of radiant heat, they reflect the heat back into the flask thus reducing the loss of heat to the surroundings.
5. Due to reduced heat loss, a thermos flask keeps the hot things hot and the cold things cold for a long period of time.

Hence, thermos flask is a special bottle that is used to keep liquids hot for a long time.