Question

Which of the following minimizes the transference of heat in a thermos flask?
1. Conduction
2. Convection
3. Radiation
(A) 2 and 3
(B) 1 and 2
( C) 1,2 and 3
(D) 1 and 3

Answer 1

Hint: Due to collision between microscopic particles some of the internal energy is transferred between them is called thermal conduction. Here the transfer of heat is due to the direct contact. Whereas convention is the phenomenon of transfer of heat through movement of liquid or gas. And thermal emission takes place in the case of radiation.

Complete step by step answer:
A thermos flask has an evacuated double walled vacuum space, which is silvered inside. Flask has a stopper that can prevent air entering and leaving. The surrounding case of the thermos flask gives an insulation to the flask.
Hence, in the thermos flask the heat transfer is prevented by radiation, because it has a silver coating on the inner bottle. The convection prevents the heat because of the vacuum between the double walls. The thin layer made up of glass walls stops the heat transfer by conduction. The surrounding case of the thermos flask gives an insulation to the flask. Thus thermos flask is an example of a device with minimum heat loss due to conduction, convection and radiation.

So, the correct answer is “Option C”.

Note: Thus the transference of heat in a thermos flask is due to conduction, convection and radiation. And these three phenomena are responsible for the minimized heat loss in a thermos flask. In the thermos flask the heat transfer is prevented by radiation, because it has a silver coating on the inner bottle. The convection prevents the heat because of the vacuum between the double walls. The thin layer made up of glass walls stops the heat transfer by conduction.