Light Bulbs

davegage
Posers and Puzzles 13 Mar '04 08:31
1. 13 Mar '04 08:31
This is a relatively easy thought experiment (probably many of you have already seen it in some form)

Suppose there are two rooms -- room A and room B. They are isolated from each other but are in close proximity to one another. In Room A there are 3 light switches. In Room B there are 3 light bulbs (everyday 120V 60W soft white bulbs). Each switch controls one and only one light bulb; additionally, each bulb is controlled by one and only one switch (1-to-1 mapping between bulbs and switches). Initially, the switches are all off and the bulbs have not been operated before.

Starting in Room A, you are allowed to actuate the switches in any way you choose; but you are only allowed to visit Room B once. How can you tell which switches control which bulbs?

I should say that there are several correct answers to this, but probably one that stands out as most obvious. Also, this problem theoretically can be generalized to more than just 3 switch/bulb pairs. For instance, 4 switch/bulb pairs would be almost just as easy as 3.
2. Asher123
Drunken Shogun
13 Mar '04 12:19
you go in and feel which lightbulbs are hot
3. 13 Mar '04 12:50
what Asher said.... specifically, you flick switch 1 on, leave it for long enough to heat up a bulb, flick it off, flick on switch 2 on and then enter the room..
hot+off=sw1
on=sw2
cold+off=sw3
ðŸ™‚
4. 13 Mar '04 21:35
yeah exactly. there are many ways to do it. for example you could also flick on all three switches, then turn each off sequentially with some period of time inbetween each off flick and then just feel which bulb is hot, hotter, and hottest. so this can easily be extended to any number n of light bulbs theoretically. for example, if you leave one switch off permanently and leave one switch up permanently, then the answer i gave above for n=3 is exactly equivalent to the case of n=5.
5. 16 Mar '04 03:33
Originally posted by davegage
yeah exactly. there are many ways to do it. for example you could also flick on all three switches, then turn each off sequentially with some period of time inbetween each off flick and then just feel which bulb is hot, hotter, and hottest. so this can easily be extended to any number n of light bulbs theoretically. for example, if you leave one switch ...[text shortened]... h up permanently, then the answer i gave above for n=3 is exactly equivalent to the case of n=5.
You cannot forget human error. First, you must note that a human can only estimate which lightbolb is hotter through its relative heat to another, yet, lightbolbs get too hot for a human to gage its relative heat to another without burning their hands. Second, even if it were cool enough to where the human could keep his hand on the bolb, he is still only estimating (guessing) which one is hotter.
Your theory is correct only as long as n is relatively small.
6. 25 Jun '04 19:55
How many dyslexics do you need to change a bight lulb?

(It's amazing how many people say, &quot;I don't know.&quotðŸ˜‰