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JAMB Physics 1992 Question 19

Question 19

Heat Transfer

The space between the double glass walls of a thermos flask is evacuated and the two surfaces facing the evacuated space are silvered. The residual source of heat loss takes place by

  1. A.convection
  2. B.radiation from the surfaces
  3. C.conduction through the stopper and the glass
  4. D.conduction across the walls.
Show the answer and explanation

Answer: C (conduction through the stopper and the glass)

Explanation

The vacuum stops conduction and convection across the walls and the silvering cuts radiation, so the heat that still escapes leaks by conduction through the stopper and along the glass.