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Two similar kettles containing equal masses of boiling water are…

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PHYSICS

Two similar kettles containing equal masses of boiling water are placed on a table. If the surface of one is highly polished and the surface of the other is covered with soot, which of the following observations is correct?

A. The two kettles will cool down at the same rate

B. The polished kettle cools down more quickly by conduction

C. The kettle covered with soot cools down more quickly because it is a good radiator of heat

D. The kettle covered with soot cools down more quickly by the process of heat convection.

QUICK ANSWER…

C

DETAILS…

Polished surfaces are bad radiators and absorbers of heat, this is why most flasks are usually coated with silver to reduce heat loss by radiation.

What am trying to say here is that a container whose inner and outer surfaces are polished will retain and prevent heat loss or transfer between its content and the environment.

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What this implies is that:

  • The kettle covered with soot will lose heat faster than that which is polished.
  • The faster loss of heat by the soot-covered kettle will be by radiation since unpolished surfaces are good radiators of heat.

Now for the right answer to the above question:

  1. Option A is incorrect. the two kettles will not cool down at the same rate because one is polished while the other is not.
  2. Option B is incorrect. no, polished surfaces are poor radiators of heat, and so, will cool down slowly.
  3. C is correct.
  4. D is not the correct answer. the concept of polished surfaces applies to heat loss by radiation and not by convection.

KEY-POINTS…

You may please note these/this:

  • A polished surface will retain more heat than a non-polished surface.

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/ culled from 2015 JAMB-UTME physics question 20 /

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