Questions of Multi-Topic Heat Transfer - Questions at the end of the chapter - Chapter 7 Class 7 - Heat Transfer in Nature (Curiosity)

Last updated at May 3, 2026 by

Q2 (Medium): Why do we see a 'shimmer' or mirage on hot days above roads or desert sand?

Answer:
We have studied that hot surfaces create convection currents and light bends through different air densities . This creates mirages:

  • Hot road heats air layers differently
  • Light rays bend through varying air densities
  • Convection currents make shimmering effect visible
Mirage Formation Process Step 1 - Surface heats Hot road creates heated air layers Step 2 - Density varies Air layers have different densities Step 3 - Light bends Light rays bend creating mirage Shimmer effect appears!

Q6 (Medium): How does a thermos flask keep liquids hot or cold for a long time?

Answer:
We have studied that heat transfers through conduction , convection , and radiation . Thermos flasks prevent all three:

  • Double walls with vacuum prevent conduction
  • No air in vacuum stops convection
  • Shiny surfaces reflect radiation back
Thermos Flask Heat Prevention Stops Conduction Vacuum between double walls Stops Convection No air to carry heat Stops Radiation Shiny surfaces reflect heat
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