Three switches and one bulb
Asked at IMC, Akuna
There are three light switches in a hallway downstairs. Exactly one of them controls a single incandescent light bulb in a room upstairs; the other two are connected to nothing. All switches start in the off position.
You may flip the switches as much as you like while downstairs, but you may make only one trip upstairs to inspect the bulb. When you go up, the door closes behind you and you cannot see or hear the switches.
Determine which switch controls the bulb.
Show a hint
A light bulb gives off more than just light.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.