Which of the following statements about heat loss in a thermos flask is incorrect?

JAMB Physics 2023 340 views
Source: JAMB · 2023

Which of the following statements about heat loss in a thermos flask is incorrect?

  1. The vacuum between the inner and outer walls minimizes heat loss by conduction.
  2. The reflective coating on the inner walls minimizes heat loss by radiation.
  3. The tightly sealed lid minimizes heat loss by convection.
  4. The vacuum between the inner and outer walls prevents heat loss by radiation. ✓
Explanation

A vacuum stops conduction and convection, because there are no particles to carry heat. But radiation needs no medium and crosses a vacuum easily.

So the claim that the vacuum prevents heat loss by radiation is incorrect. The shiny coating is what reduces radiation, by reflecting heat back.

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