You are on the 1^st floor. There are 3 light switches to choose from. You can leave only one on at a time; else you will blow the fuse. You only have time to go upstairs once to verify which switch operates the light before the rescue team abandons their search. There is no other way to verify which switch operates the light, you have no mirrors or other gadgets to cheat with, and you can only see the light bulb from the third floor or from an aircraft. You cannot just keep flipping switches and hope the pilot will see the light, because the electrical system is delicate and unstable, you may blow a fuse.

How will you verify which switch is the correct one?