Question

Draw a neat, labelled diagram of a thermos flask. Explain how the loss of heat by all three modes of heat transfer is minimised in a thermos flask.

Accepted Answer

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.

Draw a neat, labelled diagram of a thermos flask. Explain how the loss of heat by all three modes of heat transfer is minimised in a thermos flask.

Important Questions on Semester Test Paper (Chapters 1 to 10)

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