[bonanova]

You've heard this one before.

There's a light bulb in the attic connected to one of 3 switches on the wall downstairs.

You can do anything you want with the switches, make one trip to the attic and determine which switch controls the bulb.

It's impossible to choose among three options with only 1 bit [on/off] of information, so you add another bit [warm/cold] to the mix:

1. turn switch 1 on, turn switch 2 on, leave switch 3 off.
   
2. Wait five minutes and turn switch 2 off.
   
3. Go to the attic.
   
4. Bulb on - it's switch 1.
   
5. Bulb off and warm - it's switch 2
   
6. Bulb off and cold - it's switch 3
   

Cute solution. That's the old problem. Here's the twist: the bulb is out of reach.

You can't feel it, and you don't have infrared telemetry.

So you can't distinguish off and warm from off and cold.

Can you still determine which switch controls the bulb?

[Brandonb]

You can't feel it, and you don't have infrared telemetry.

So you can't distinguish off and warm from off and cold.

Can you still determine which switch controls the bulb?

Moths in the attic?

[Guest]

why not just take shoelaces, shirt string whatever you are wearing, and tie it to switch two. Turn switch 1 on. Go to the attic if no light pull the string. If no light. then it's 3

[Guest]

Just install a dimmer switch, =D

Edited October 17, 2008 by telethar

[Guest]

Use the same method as before but since you cannot touch the bulbs use water instead. if the water evaporates quickly its switch two. If not its switch 3.

[Guest]

Turn switch 2 on and off repeatedly for a while. This will eventually cause it to burn out (hopefully), and then you can (again, hopefully) see which bulb is burned out and which is just turned off to distinguish between 2 and 3.

Or else just get a ladder and do it the regular way.

[Prime]

One way, or another you need a third state.

Leave your camcoder running in the room.

[peace*out]

turn on one for 10 min.

2nd for 2min

3 for 0.

turn the light of and see which one glows the brightest, 2nd , and not at all.

[Guest]

turn off all electricity using devices in the house,check the power consumption on the meter for a baseline, turn on 2 switches wait 2 weeks , check the power consumption on the meter, if it has gone up then turn one switch off and wait two more weeks if it goes up the one that's on is the switch , if not then the other one u turned on then off is , and if no electricity was used then the third switch is it ... then go up to the attic if you want rewire the electrical so you can have a switch in the same room as the bulb because to do otherwise is idiotic

and the way I heard this one before is that there were 3 switches and 3 bulbs , but it still ends up being the same problem and solution... although my solution wouldn't work if there were 3 bulbs , or 2 for that matter

[Guest]

This is fun, but I am baffled, so here are a couple of ridiculous solutions:

Setup a camera in the room to take a picture every minute. Turn on each switch, one at a time, for one minute. The pictures should indicate which switch activated the bulb.

Build a small solar powered vehicle that will travel exactly 3 feet per second whenever it is in sufficient light. Cover any windows with a blanket, and place the vehicle on a marked place on the floor. Turn on switches 1 and 2. After 2 seconds, turn off switch switch 1. After 2 more seconds turn off switch 2 (if you wish, not really necessary). If the vehicle has moved 6 feet, switch 1 controls the bulb. If the vehicle has moved 12 feet (or all the way across the room if you left the switch on), then switch 2 controls the bulb. If the vehicle has not moved at all, either switch 3 controls the bulb, or the bulb is burnt out

Affix a small motor to a wheel. Attach one end of an arm to one side of the wheel and the other end of the arm to the tip of switch 2 so that turning on the motor will cause the wheel to spin, and the arm will travel up and down switching the light on and off (yes, I realize you will need some joints and such, but you get the idea). Turn on switch 1. Activate the motor. If the bulb is constantly on, switch 1 controls the bulb. If the bulb flashes on and off, then either switch 2 controls the bulb, or you have a very strange bulb, or there is a major short in the wiring in your house, and you should probably leave before it catches on fire. If the bulb is not on at all, either switch 3 controls the light, or the bulb is burnt out.

[bonanova]

Great ideas all - nice going.

I want to respond to what's come in while keeping it open for more replies.

So I'll put it into a couple spoilers.

I kind of liked this puzzle - it sparked some creative responses even though it didn't relate to probability or infinity in any way!

In grading the replies I looked for creativity that nevertheless respected the parameters laid out in the OP, which, briefly are these:

1. Attic bulb connected to one of 3 switches downstairs.
   
2. Do whatever you want with the switches. THEN
   
3. One trip upstairs
   
4. Determine which switch controls the bulb
   
5. Don't use heat as a criterion
   

Post 3: blades575 - using shoestring to flip switch AFTER going upstairs. Sequence of action is wrong.

Post 5: wahledor - use evaporating water - violates point [5] of OP.

Post 8: peace*out - differential "glowing" - also violates [5] of OP.

Post 7: Prime - camcorder needs initial setup - can't be implemented in one trip upstairs - violates [3] of OP

Post 9: cykodryver - repeatedly read the power meter. No good unless meter is upstairs, then would violate [3].

Post 10: tamjap - camera, like Prime's camcorder violates [3]. Solar vehicle [but I loved that idea ] also needs initial setup so violates [3].

Grand prize for out-of-the-box-ness, but not fleshed out completely:

Post 2: Brandonb: Moths!!! I guess you could turn switch 2 on for a long time, turn off, turn switch 1 on and race upstairs.

If burning, it's switch 1. Otherwise, if dead moths, or any moths, are nearby, it's switch 2. Otherwise it's switch 3.

Beautiful approach that fails only if there are mothballs nearby.

Prizes for literal responsiveness to OP:

Here the operative OP guidance was "you can do anything you want with the switches"

And I still have to rule out blades575, because the "doing" has to PRECEDE going into the attic.

But these three are winners: In the order posted,

Post 4: telethar - swap switch 2 [say] with a dimmer switch. Note that seeing a dimly lit bulb relies on light, not heat, so OK.

Post 6: Chuck Rampart - Flip switch 2 [say] repeatedly until the bulb would be expected to have burned out.

Post 10: tamjap - motorize switch 2 [say] to continuously flip. Note that although the flipping continues after you went upstairs, WHAT YOU DID was finished before you went upstairs.

I can't pick a best answer among these three.

CR's was the closest to mine [keep switch 2 on and wait a thousand hours for burnout] but faster. so better. Kudos.

tamjap - thought of his answers as ridiculous, but his third one works and respects the OP.

I guess I lean towards telethar's, tho I didn't, at first. But it's simple, responsive to OP, and effective.

[peace*out]

man - i didn't know there were so many options!!!

[bonanova]

man - i didn't know there were so many options!!!

Oh yeah ... best way to get five opinions on a subject? Ask four BD'ers!

[peace*out]

True,.................

[Guest]

Aw shucks... I was afraid that entering the room for setup would nullify the answers....

I have a question about one of the acceptable solutions:

The question involves the idea of causing the bulb to burn out. I am no electrician, so most of this is just supposition. Assuming that flipping on a standard toggle light switch just completes a connection that allows electricity to reach the light bulb, would it be possible to short circuit any breakers involved (assuming the breaker box is not in the room in question), remove the switch, and feed a current through the wiring sufficient to burn out the bulb? I realize you would need to account for AC vs DC current and such, but I assume that if you knew how to do all of that other stuph, you could figure it out.

I have to admit, though, now that I know that you're not looking for a 'right answer' and I can go nuts with ideas, I may not sleep this weekend thinking about it

[Guest]

question , if you let one switch go on long enough to burn out or flip it repeatedly how do you know which switch of the three activates the light?

because if it is the one u left on for 1000 hours and flipped one of the other two on all you know is that it's either the burned out or the switch that's off ,

it relies on probability from there basically so you'd still have 1/3 chance of getting the switch right still, and I dunno about you but I can't tell if a light bulb is burned out just by looking at it... in the dark

now if you could rig up a remote system that would flip each switch separately then go upstairs then I guess you could call that a solution but that's just lame

[Guest]

question , if you let one switch go on long enough to burn out or flip it repeatedly how do you know which switch of the three activates the light?

because if it is the one u left on for 1000 hours and flipped one of the other two on all you know is that it's either the burned out or the switch that's off ,

it relies on probability from there basically so you'd still have 1/3 chance of getting the switch right still, and I dunno about you but I can't tell if a light bulb is burned out just by looking at it... in the dark

now if you could rig up a remote system that would flip each switch separately then go upstairs then I guess you could call that a solution but that's just lame

This is true. My original response was going to be wait til burnt out, but you're right.. how do you know which is burnt out vs. which is just off? sometimes lights have that little (filament?) that falls to the bottom of the bulb, but it can be very difficult to see!

[Guest]

Because you're economically and environmentally savvy, the bulb in the attic is a compact fluorescent bulb. While CFL's last longer and use less electricity, they take a few minutes to warm up to their full brightness. So, you flip on switch one for 10 minutes, then flip on switch two and *immediately* run upstairs to the attic.

1. Light on and bright = switch one

2. Light on and dim = switch two

3. Light off = switch three

Edited October 18, 2008 by spiffmo

[bonanova]

1. How the burnout approach works:
   Switch 3 remains off
   Switch 2 is turned on and left on for 1000 hours [say] or toggled on and off a million times [say] to induce burnout, then turned off.
   Finally, switch 1 is turned on and you enter the attic.
   If bulb is off but intact, it's S3
   If bulb is burned out, it's S2
   If bulb is on, it's S1.
   
   
   
2. tamjap's query about short-circuiting things: circuit breakers are switches that turn themselves off when the current exceeds a preset amount. if you removed all breakers and switches and just connected the bulb to the service line, it would not burn out any faster than it would if normally turned on.
   
   
   
3. spiffmo's Compact fluorescent bulb suggestion:
   The OP just says "bulb", so ... if it were a CFB, that's a good solution.
   

[Brandonb]

cool, thanks bonanova!

I thought about this again, and came up with a 'duh' solution that I am pretty sure doesn't violate the OP.

Turn off everything in the house. Then, through whatever series of flips you want to make, take a trip around the house (not to the attic) and figure out what the switches turn on. If one doesn't do anything, then that's the attic light. If two do nothing, then turn one on and check the attic. If all three do nothing, then why did your electrician install a 3-switch panel for one single light?

[Prime]

I think this wouldn't violate the conditions:

Turn one switch on. Go into the attic. Unscrew one of the unlit bulbs. Go back downstairs, open up the panel with the switches and check impedance in the wire. Or turn switch on and check for the current. But not with your fingers! You can buy a special screw driver with a little bulb on it for couple bucks. This way you can save the bulb too. And it is only one trip upstairs.

[Guest]

I think this wouldn't violate the conditions:

Turn one switch on. Go into the attic. Unscrew one of the unlit bulbs. Go back downstairs, open up the panel with the switches and check impedance in the wire. Or turn switch on and check for the current. But not with your fingers! You can buy a special screw driver with a little bulb on it for couple bucks. This way you can save the bulb too. And it is only one trip upstairs.

unfortunately, the bulb is out of reach in the original problem, Prime! but i admire the creativity and knowledge of electrical systems.

bonanova: once in the attic, how can you tell the burnt out bulb from the off bulb? it's not like one explodes, right?! i think i made the same error in thinking about it. or is there something i'm missing?

maybe if you emit a high pitched sound, the glass of the bulbs will shatter and you will be able to see which filament is still intact.

[Guest]

plus there's only one bulb

[Guest]

Rip out two of the switches. Connect the outputs from these switches in parallel with the output from the one remaining switch.

That's the switch that controls the attic bulb.

[Guest]

Thought I should clarify my previous suggestion:

I meant from the switch, run more current through the wires than would normally run in a house - say push through 220 instead of regular 110. That should overload the bulb, and make it burn out much more quickly than flipping the switch repeatedly.

Have to say, though, I think I like Octopuppy's solution the best!

"Don't go out and get a piece of the pie - Make your own @#$% pie!"

[bonanova]

unfortunately, the bulb is out of reach in the original problem, Prime! but i admire the creativity and knowledge of electrical systems.

bonanova: once in the attic, how can you tell the burnt out bulb from the off bulb? it's not like one explodes, right?! i think i made the same error in thinking about it. or is there something i'm missing?

maybe if you emit a high pitched sound, the glass of the bulbs will shatter and you will be able to see which filament is still intact.

to tell if a bulb is burned out.

1. if the bulb is not frosted, you'll see the break in the filament.
   
2. often there is a black area on the inside of the bulb
   
3. you can screw it into a live socket and see if it lights.
   
4. even if the bulb is frosted, you can hear the loose filament if you shake it gently.
   
5. you can check the resistance between the screw threads and the base tip - more than a few ohms it's burned out.
   
6. you can take it back to the store and claim it's defective. Before they refund your money they will check it out.
   
7. make a high-pitched sound ... wait, you already thought of that.
   
8. you're smart; you can probably think of 6 more ways .... <_<