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Statement I: A thermos flask is made of double-walled glass bottles. Statement II: Metals are good conductors while gas and air are poor conductors of heat.

Statement I: A thermos flask is made of double-walled glass bottles. Statement II: Metals are good conductors while gas and air are poor conductors of heat. Correct Answer Both the statements are individually true and statement II is the correct explanation of statement I

CONCEPT:

  • Thermos flask: A thermos flask is an instrument that keeps hot liquids hot and cold liquids cold for long hours.
    • So it’s an ideal example of a closed system so ideally no heat is radiated/absorbed through the thermos.
    • It consists of a glass vessel with double walls. The glass vessel is enclosed by a metal or plastic cover for protection against damage.

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  • The outer surface of the inner wall and the inner surface of the outer wall are silvered (shining). The shining surfaces reduce heat loss due to radiation.
  • An insulating stopper (cork) is used to close the mouth of the vessel. The vessel is kept over an insulating (cork ) pad.
  • It is therefore thermally insulated. Hence, heat does not leave or enter easily and hot liquids remain hot while cold liquids remain cold inside the flask.

EXPLANATION:

  • In a thermos flask, we have two walls made of glass and the space between them is made a vacuum. Due to this vacuum, there is less chance of heat transfer of heat. So statement I is correct.
  • As the glass is a bad conductor of heat that’s why a silver-coated glass wall is used so that the heat transfer can be reduced. Also, the air is a bad conductor of heat and metals are good conductors of heat. So statement II is correct.
  • Thus statement II is the correct explanation for the statement I. So option 1 is correct.

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