Thursday, September 08, 2005

Can you shed some light on this problem?

A windowless room contains three identical light fixtures, each containing an identical light bulb. Each light is connected to one of three switches outside of the room. Each bulb is switched off at present. You are outside the room, and the door is closed. You have one , and only one, opportunity to flip any of the external switches. After this, you can go into the room and look at the lights, but you may not touch the switches again. How can you tell which switch goes to which light?

Hint: This one is easier than you think!


  1. So I can play with the switches any much I want BEFORE I enter the room? The wording it tipping me off but I haven't gotten it yet...

  2. Yes, you can play with the switches as much as you want before you go into the room.

    You're on the right track.

  3. turn on one light outside the room, go inside and you can see. then just use the three switches inside the room.

  4. If these are Incandescent lamps, then I would be in luck with this one. Since they give off more heat then light. I will heat up at least one lamp by leaving switch #1 on for about three of four minutes. That thing will be HOT to the touch.

    Next i can turn off switch #1 and turn on switch #2.

    I will go into the room to see what lamp coresponds to switch #2 by it being on. I will feel the two remaining bulbs for heat. The lamp coresponding to switch #1 will be hot. The remaining bulb goes to switch #3.

    if these lamps are florecent though, chances are by the time I enter the room the lamp coresponding to switch one will be cool already.

  5. Umm.. Sean, there are no switches inside the room?

  6. Karnov has the right answer. I'm not sure how quickly the bulbs will cool off, though.


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