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Google Talk Riddle 2: Which Switch?

by William Jackson on 2007-03-07

Todayʼs Google Talk Riddle was:

You are in a room with three switches. Upstairs in a closed room is a single lamp with a normal bulb that is controlled by one of the switches. You must determine which switch controls the lamp. Once you go upstairs, you cannot return to the switches. How do you do it?

It was posted at 10:38 Central Standard Time.

The first correct answer came in at 10:54, courtesy of my friend Sol. This was his method:

Turn on the first and second switches and wait for a while. Then turn off the second switch and go check the lamp. If the lamp is on, the first switch controls it. If the lamp is off, feel the bulb. If the bulb is hot, the second switch controls it. If the bulb is cool, the thirdswitch controls it.

An alternate, but essentially identical solution provided by my brother Eric is to turn on the first switch, wait a few minutes, then turn off the first switch, turn on the second switch and immediately go check the lamp. This is the solution I was aware of.

I am going to continue to release these Google Talk Riddles regularly, and the only place I will release them is in my status message on Google Talk. Because I only have a limited amount of space for the message, they are often abbreviated versions. I try to leave in all the essential information, but feel free to ask questions. I will answer to the best of my ability without revealing the solution.

Also, if you tell your friends about it and they want to add me as a contact, please either let me know or have them send me an email, so I recognize the email address when I receive a contact invitation.