257 replies to this topic

[rookie1ja]

Bulbs - Back to the Logic Puzzles
There are three switches downstairs. Each corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position.
How would you identify which switch corresponds to which light bulb, if you are only allowed one trip upstairs?


This old topic is locked since it was answered many times. You can check solution in the Spoiler below.
Pls visit New Puzzles section to see always fresh brain teasers.

Spoiler for Solution

Bulbs - solution
Keep the first bulb switched on for a few minutes. It gets warm, right? So all you have to do then is ... switch it off, switch another one on, walk into the room with bulbs, touch them and tell which one was switched on as the first one (the warm one) and the others can be easily identified ...

Spoiler for old wording

This is one of my favorite logic puzzles (Edit: it is more a practical than a logic puzzle).
Imagine you are in a room with 3 switches. In an adjacent room there are 3 bulbs (Edit: let's say in lamps which are on a regular table) - all are off at the moment, each switch belongs to one bulb. It is impossible to see from one room to another. How can you find out which switch belongs to which bulb, if you may enter the room with the bulbs only once?

Edit: No help from anybody else is allowed.
Edit: Find out which switch belongs to which bulb - identify all 3 switches (so find out what bulbs are switches 1, 2 and 3 connected to)

[bgailer]

I don't think LED bulbs get discernibly warm.

[phoenixblaze]

Turn on all the switches and you'll know what color all the bulbs are.

[kolonel]

You only need to turn on 1 switch as each switch belongs to one bulb. That one bulb will come on no matter which switch you turn on.

Regards
kolonel

[planeterry]

Assuming that there is some sort of doorway/passageway between the rooms, and that the rooms are next to each other (and also assuming that the bulbs are not arranged in a straight line as observed from that doorway).....then you can tell which bulb is on by simply observing the shadow is being cast through the doorway by the bulb. Maybe this is personal...but walking into the room and touching a HOT bulb that has just been turned off does not sound like much fun to me.

[qazqaz]

Maybe this is personal...but walking into the room and touching a HOT bulb that has just been turned off does not sound like much fun to me.

that is not personal...

[jahash]

Alternatively:
-1 switch off = bulb off
-1 switch on = bulb on
-1 switch halfway (yes you can do this) = bulb dim & flickering

[Compumyst]

You could also walk into the room and have someone else turn on/off each switch. It never said you couldn't recruit help.

[Garrek99]

There is a little problem in the way that the puzzle is introduced.

You say that this is one of your favorite "logic" puzzles.
But the minute I read "logic" and your "favorite" it brought out the big guns. I worked on a purely logical solution for almost 2 weeks and obviously there isn't one because the solution is a prctical solution not a "logical" one.

Now, I know that all puzzles are logic testers but to label a puzzle a "logic" puzzle is to suggest that the solution is not worldly.

I want my 2 weeks back. lol

[fosley]

Walk into the other room and remove all bulbs. Now you know that none of the switches is connected to any bulb.
Alternately, you could disconnect the switches, put batteries of specific voltages on each wire, then test each socket to see which one is connected to which battery.

I agree that "logic puzzle" and "touch the warm bulb" seem a little not synonymous, but I want to thank you for this, because I used this trick to troubleshoot my brake lights (it's hard to view the bulb while sitting in the car pressing the brake pedal). I could have wedged something between the brake pedal and the seat, but I figured this would be easy enough, and it worked.