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The 3 Switches Puzzle (and solution)

The 3 Switches Puzzle (and solution)

Can you solve the “3 Switches” puzzle? You are in the basement of a house where there are are three identical on-off switches.  One of them controls a lamp in the attic, and two of them do nothing.  You have no way to see into the attic or to see reflected light from the attic.

Can you solve the “3 Switches” puzzle?

You are in the basement of a house where there are are three identical on-off switches.  One of them controls a lamp in the attic, and two of them do nothing.  You have no way to see into the attic or to see reflected light from the attic.  If you go upstairs to the attic, you are not allowed to return to basement.

You are permitted to manipulate the switches all you like, but you are only allowed one single trip to the attic.

Question:  Which switch controls the lamp?

Scroll down for the solution…

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The Solution:

Switch on switches 1 and 2, wait a minute and then switch off number 2.

Now go upstairs to the attic to check the lamp.

If the bulb is on, then you know switch 1 is wired to the lamp (since you turned off switch 2 and never turned on switch 3).

If the bulb is off and hot, then you know that switch 2 is wired to the lamp (since you left it on for a minute, enough time for it to get hot, but then turned it off).

If the bulb is off and cold, then you know that switch 3 is wired to the lamp (since you never turned on switch 3 at all).

And now you know.


Note:  This works best if there’s an incandescent bulb in the lamp and not an LED.  Most LEDs do not give off much heat, so it would be harder to notice the difference in temperature (especially if you had trouble getting up the stairs and it took you a while to get to the attic!).

the more you know

 

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