# You have 'three' lights.. (Thats more than Ratch's puzzle:)

Discussion in 'Physics' started by triggernum5, Jul 23, 2008.

1. ### triggernum5 Thread Starter Senior Member

May 4, 2008
216
1
This is just a pretty old puzzler, so refrain from spoiling it if you already know it please..
There are 2 rooms that are completely isolated from each other. In 1 room, there are 3 light switches. In the other, 3 light bulbs.
How can you determine which light switch is connected to each light bulb if you can only be in each room ONCE?

2. ### jpanhalt Expert

Jan 18, 2008
7,218
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Does each switch only work one bulb? Is each bulb identical in wattage, etc.?

John

Jul 23, 2008
110
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once only?

4. ### linchiek Active Member

Jul 23, 2008
110
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can i send some1 to the other room with a walkie talkie?

5. ### triggernum5 Thread Starter Senior Member

May 4, 2008
216
1
Yes, you can be in each room only once, and the lights are each controlled by a single isolated switch..
And oh, did I mention the rooms were lined with lead and adamantium? Impenetrable to RF, and cabling..
Oh, and you aren't allowed to seek assistance from the Asgard, or any other alien race..
Oh, and no time machines.. You're stuck with current human technology, the rooms are rigged to explode if any disturbances in the space-time continuum are detected..

I will add that the switches are wired properly.. Up is ON for each switch..

6. ### jpanhalt Expert

Jan 18, 2008
7,218
1,600
I've got a solution. Should I post it or what? Don't want to ruin the fun for everyone else. Clue: visit the room with the lights first.

John

7. ### linchiek Active Member

Jul 23, 2008
110
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take off the 1 of the light bulb?

8. ### jpanhalt Expert

Jan 18, 2008
7,218
1,600
So now, you have only one degree of freedom. What can you do to reduce that to define the system? John

9. ### triggernum5 Thread Starter Senior Member

May 4, 2008
216
1
I'm interested in your solution, I don't see how your hint would lead to the solution I know..

Here is a hint.. Not long from now the solution I have may be nearly obsolete..

10. ### thingmaker3 Retired Moderator

May 16, 2005
5,073
8

0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

Obviously, the 000 and 111 won't tell us anything. Each of the other combinations will certainly reveal a connection between one switch and one luminaire. Beyond that, I'm lost.

I will observe, however, that in order to be in each room only once, there must be a passage between the rooms and a second egress in each room. I would therefore proceed by grabbing my hard-hat light, glow-rods for fishing the walls, a flexy-bit & drill-motor, and my belt-tools. I'd turn off the appropriate breaker first, and then re-wire the place with one luminaire in each room controlled by three-way switches at each door. Upon exiting, I would turn the breaker back on and disclose, with perverse confidence, which switch controlled which luminaire.

I would, of course, have my spoon with me at all times. (Just in case Ratch or someone else showed up with a hollow ball. Or a solid ball. Or a quince.)

11. ### triggernum5 Thread Starter Senior Member

May 4, 2008
216
1
Its an adamantium room (The metal Wolverine's claws are made of).. You can't rewire it.. Doesn't matter if you have a spoon, or even a towel..
To clarify, you begin in a hallway with 2 rooms off it.. One room is labeled switches, the other labeled lights..
And I know your intentions are good, but c'mon.. If anybody was dumb enough to design a setup like that for usability, do you really think they'd be able to figure out how their lights worked after your changes?

Hint: Think 0 0 1, 0 1 0, and 1 0 0.. But don't forget 0 1 1, 1 0 1, and 1 1 0..

12. ### jpanhalt Expert

Jan 18, 2008
7,218
1,600

Danger: This method is intended for use only with conventional incandescent light bulbs. If the bulbs are CFL, you will need to modify the method.

1) Get two helpers and a ladder and go to the room with 3 bulbs. Identify the bulb placement and assign an identifier to each bulb (like 1,2,3).

2) Do nothing to bulb #1

3) Place the ladder under bulb #2, climb the ladder, hold the bulb, and have your assistants turn the ladder until you have completely removed the bulb.

4) Place your ladder under bulb #3 and repeat the steps described in step 3 to remove it. Carefully remove the glass part of the bulb. No hints on the best way to do that, but you do have two assistants to help the brain trust.

5) Reverse the process for bulb removal and replace the bare bulb #3.

6) Go to the switch room. Put an ammeter in series with switch A. If the current stays on, then A=1; if there is no current, then A=2; and if there is a short burst of current, then A=3. And so forth for the remaining switches.

NB: One could also short (e.g., with a penny) one set of contacts in a socket, or put two bulbs in series, etc. and get pretty much the same logic. Shorting could be used for CFL and might give a more exciting result.

If an ammeter is are not allowed, the walkie talkie could be used to detect which switch has current from the hum, assuming it is AC. Also, the more exciting short circuit approach should be obvious.

John

Edit: I have assumed an "all on" or "all off" initial state. It should also work, if the on-off positions of the switches are not labeled (for example, "lever up" may be "on" for one switch and "off" for another). If that is not the case, then one can use the information that only two switches are in the same state to define the system (reduce DF to 0) by unscrewing just one bulb.

Last edited: Jul 25, 2008
13. ### linchiek Active Member

Jul 23, 2008
110
0
i got simpler explanation since u said its incandescent light bulbs...

1. turn on switch A for 5 mins, then switch off
2. turn on switch B and do nothing with switch C.
3. go to the next room

solution:
the bulb with light is control by switch B,
the warmer bulb (not lighted) is control by switch A, and
the coolest bulb (not lighted) is control by switch C......

14. ### linchiek Active Member

Jul 23, 2008
110
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incandescent light bulbs produce heat more than fluorescent light....

15. ### linchiek Active Member

Jul 23, 2008
110
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since it's pretty old puzzler, the light bulb shud be incandescent light bulbs rite?

16. ### jpanhalt Expert

Jan 18, 2008
7,218
1,600
@linchiek
Sounds good to me, assuming you can tell when a switch is on or off. John

17. ### linchiek Active Member

Jul 23, 2008
110
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just label the switches A, B, C b4 u proceed with the step that i mention...

18. ### linchiek Active Member

Jul 23, 2008
110
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i want a SPOON too.......

19. ### jpanhalt Expert

Jan 18, 2008
7,218
1,600
I think you missed my point. Labeling the switches A,B,C will not tell you whether each one is on or off. My solution has the same problem. That is, you need a way to tell whether a switch is on or off from the switch room. If the initial state is all on or all off, it is not such a problem.

For example, assume the "warm" bulb switch is initially on. Not knowing it was on, you end up turning it off for 5 minutes, then change its state back to what will be "on". Another bulb is initially off, you change its state to "on." Now, when you go to the room, there will be two bulbs lit.

John

20. ### thingmaker3 Retired Moderator

May 16, 2005
5,073
8
I think Linchiek's solution would indeed work for incandescent bulbs. They're little space heaters, after all - light is a just their by-product. Even compact fluorescents get warm after a while.