In front of you are three light switches. Only one switch works, and it turns on the light downstairs.

From where you are standing, you can’t see the downstairs light, and it makes no sound.

You must determine which switch operates the light, BUT you can only check it once.

How do you figure out which switch is for the light?

Here’s the answer:

It takes 2 flicks of the switch and a portion of the time you can’t get back.

Did you get it right?

Workings:

Light bulbs convert electricity into light and heat, right? So, it doesn’t matter which switches you turn on or in what order. Try one and wait 5-10 minutes. This should be enough time to warm up the light bulb if it is on. If it’s not that one, the light will be off and cold right?

Click the second switch. Wait another 5-10 minutes.

Now go and check. If the light is on, great, you know it’s the second one. If it is off but hot, then you know the first switch was the one that worked. If it’s off and cold (assuming it won’t lose its “heat” in the time that’s passed), then neither of the first two worked, and the working switch must be the last, un-flicked one.

Or you could trace the wiring, whatever.