In a summer heatwave, keeping curtains drawn all day helps cool the room. The physics: solar energy passes through windows and is absorbed by curtains. The curtains heat up until they radiate as much heat as they absorb. They radiate 50% back toward the window and 50% into the room. Thus curtains stop 50% of solar energy.
Today's Puzzle
Imagine a room with roller blinds and curtains. The blinds line the windows, and the curtains cover the blinds—two layers of protection. What percentage of the Sun's energy gets into the room?
At first glance, you might expect the blinds to pass on 50% to the curtains, and the curtains to radiate 50% of that into the room, giving 25%. Incorrect! Think like a physicist. Consider the heat flow and equilibrium of the sun-blinds-curtain system. No complicated equations required. Assume blinds and curtains are homogeneous.
Discussion
No spoilers please. Instead discuss blinds vs curtains. The solution will be posted at 5pm. Thanks to Alan Williams-Key for today's puzzle.
