The UAFC

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 can only go into the room and look at the lights once, but you may not touch the switches again once you do. How can you tell which switch goes to which light?

Guess you could turn two on for a while. then turn one off.

You've now a cold bulb - the one you didn't turn on,

a hot one the one that was on and is now off,

and a lit one - the one that is currently switched on...

OUCH! burnt my hand touching the hot bulb!