Question

Draw a labelled diagram of a thermo flask. Explain how the transfer of heat by conduction, convection and radiation is reduced to a minimum in it.

Answer 1

Heat transfer is minimised because of:
(1) The vacuum between the two walls, rubber, glass, cork and air do not allow the loss of heat by conduction.

(2) Cork in the neck of flask and the cup over it prevent loss of heat by convection.

(3) Heat cannot be lost by conduction or convection because of vacuum between the two walls.

(4) Heat loss is also minimised by radiation, by making outer surface of inner wall and inner surface of outer wall silvered. The inner wall is a BAD RADIATOR and the outer wall is a GOOD REFLECTOR of radiation.