Problem Graphic


Max is playing in the backyard, focuses the sunlight with a magnifying lens to burn peanuts in a sieve, which his mother left in the sunlight for drying. His mother shouts to him "Be careful! Do not burn yourself!" Max shouts back "Ok. How hot is it? Can I boil water with the lens?" Max's mother knows that the solar system using the sunlight can boil water. But she has no idea how hot the focus can be. That is, what is the upper limit of the temperature the focusing sunlight system can reach? Can you help her?

What is known:

Focusing the sunlight with a magnifying lens


  Can this focus be made hotter than the sun itself?

  • Assume this focus can be hotter than the sun itself
  • Use the second law of thermodynamics to verify the assumption