ECN Forum Forums General Topics of the Trade General Discussion Area Brain teaser

This one was told to me by a plumber today at the jobsite. Its easy I figured it out

You have 3 lights up in the attic of a building. These 3 lights are controlled by 3 individual switches in the basement of the building. You must identify which switch controls what light BUT, you can't obviously see the lights from the basement.
How do you identify what light is controlled by what switch without the use of any tools except maybe a stepladder if needed to reach the lights, and with only making ONE trip from the basement to the attic. Assume the lights could have just recently been on and might still be hot.



A.D

Aw! You should edit out your last sentence.

(the last sentence gave the clue)

I deleted my post so others can have a chance at guessing it.

[This message has been edited by Sixer (edited 10-26-2006).]

[This message has been edited by Sixer (edited 10-26-2006).]

Turn sw#1 on and leave it on for 1 minute.
Then turn it off.
Turn on sw#2 and leave it on.
Goto attic and climb ladder.
Feel the off bulbs. The hot one is on sw#1
and the other is on sw#3.

I heard this one on Car Talk....

Step 4 re-wire lights to one switch and locate switch near attic access!!

It was an easy solution but I started wondering how MacGyver would've done it. I'm pretty sure he would've started by taking apart the clothes dryer. He might also have left the switch on and looped a string with a weight, secured to the rafter, around the handle. The can of spray starch would act like a blow torch ,(see also: James Bond, "Live and Let Die" venomous snake application), on the string. This would create a precise, for MacGyver, time delay, allowing ample transit time to the attic. Now, if he can only help Dana Elcar grow his hair back and get him to stop picking on Pappy Boyington!
Joe

One of the bulbs has been 'borrowed' by a sheetrocker: How many trips to the attic do you need to do to be 100% sure which switch operates which bulb?

Alan

Make one trip up there and install a camera?

Well, if neither of the two remaining bulbs is on, but one is warm, the missing bulb must be the one that's "on". Vefify by taking one of the two remaining bulbs to try it in the empty socket, it should light. You don't have to leave the attic. One trip

Or if one is on, and the other is warm, then the missing bulb is the one that was always off. Or if the dark bulb is cold, then the missing bulb was the one that would have been warm. One trip

BUGGER!
I should have edited out that last sentence!!
But you are all right. Thats how it is done.

A.D

None! You tell the sheetrocket to go up to the attic and "hold" the empty lampholder up with his finger inside the screwshell.

When you hear a crash and cursing, you know you've found the switch for that light!

Go up to the attic one time and install three different wattage lamps taking note of which lamp is in which socket, go back down and use an ammeter to see which switch operates which lamp.

Roger

How many light bulbs does it take to change an electrician?


Three.

Eventually the Boss gets cheesed and fires yo' ass.

why would you even install three sisdeby side lights in the attic?

Too bright.

Edward

It's all moot because any electrician installing 3 switches in the basement for three lights in the attic, would have installed 2, 4-ways in the attic stairwell just to jumble the order and keep things interesting. 2 of the basement switches would be able to be switched to control any of the three bulbs while the other could switch 1 of 2. It could be a great shell game for the kids.
Joe