You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

Solution: Turn on the first 2 switches and wait 5 minutes. Turn off one and go through the door. The light shining is the switch you left on. Now of the other two off lights one is still warm that will be your second switch which is now off. The third is a cold light and therefore the switch you didn't play with at the start.

Ta da!