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        riddles >> easy >> 4 light bulbs
        
(Message started by: Iceman on Aug 11^th, 2007, 7:03am)

Title: 4 light bulbs
Post by Iceman on Aug 11^th, 2007, 7:03am

This riddle is a similar version of the 3 light bulbs riddle, and everything is the same, except for the fact that there are 4 light bulbs and 4 switches. Have fun!

Just in case someone isn't familiar with the riddle, here is the link of a recent one (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_easy;action=display;num=1180944678).

Title: Re: 4 light bulbs
Post by denis on Aug 11^th, 2007, 10:03am

I assume all switches are off to begin with.

Label the switches A,B,C,D. Turn on switch A and B. Wait ten minutes, then turn off switch B and turn on switch D. Go immediately in the room:

The bulb that is on and hot is A
The bulb that is on but just starting to warm up is D
The bulb that is off and cool is C
The bulb that is off but still hot is B

Title: Re: 4 light bulbs
Post by Grimbal on Aug 11^th, 2007, 2:44pm

Switch them all on for 10 minutes.
Turn off A, B, C, D in turn, waiting a minute between each.
Go to the room and make a precise measurement of the temperature. From coldest to hottest, you get A, B, C, D.

Title: Re: 4 light bulbs
Post by Iceman on Aug 15^th, 2007, 7:30am

on 08/11/07 at 10:03:00, denis wrote:

I
The bulb that is on but just starting to warm up is D

Yep, that could work, but then you have to rush in the room like the wind. I propose a bit different approach. So, at a particular moment, you turn on one switch, wait for 20-30 seconds or so, and then turn it off. Like this, a narrower part of the glass bulb heats a bit more quicker, and it cools down significantly more slower, as the bigger part of the glass bulb is not that warm. The difference is obvious, or at least, it was with two different bulbs I have tested that way. :-/ ;)

Title: Re: 4 light bulbs
Post by Grimbal on Aug 15^th, 2007, 7:33am

If the room is very large, so large in fact that the light of the light bulbs needs minutes to reach the door, I can think of another solution. ::)

Title: Re: 4 light bulbs
Post by Iceman on Aug 15^th, 2007, 7:51am

Perhaps this riddle isn't over. :o ::)

Title: Re: 4 light bulbs
Post by Death on Aug 16^th, 2007, 4:34pm

Grimbal, would this consist of you [hide]turning each of the switches on and off again, walking into the room and the first lightbulb you see turning on is the first switch, the secong bulb is the second switch, etc.[/hide]

Of course the problem is then that the lightbulbs would be too far away to distinguish but that can be overcome by [hide]having them in 4 corners of the room and the door that you go through as a trap door.[/hide]

I realise that this is massively complicated but at least it's something. ;D

Title: Re: 4 light bulbs
Post by Iceman on Aug 16^th, 2007, 4:39pm

Death, you are killing me. :P :-*

Title: Re: 4 light bulbs
Post by Death on Aug 16^th, 2007, 4:59pm

I try my best :P