View Full Version : Brain teaser # 5
Four switches can be turned on or off. One is the lightswitch for the incandescent overhead light in the next room, which is initially off, but you doon't know which. The other three switches do nothing. From the room with the switches in it, you cant see whether the light in the next room is on or off. You may flip the switches as often and as many times as you like, but once you enter the next room to check on the light, you must be able to say which switch controls the light without flipping the switches any further. ( And you cant open the door without entering, either).How can you determine which switch controls the light?.This is not a trick question but does require thinking outside the box.
If a switch is turned on or off, it usualy makes a slight poping sound and would indicate that current was flowing.
Since the other three switches do NOTHING, there would not be the poping sound.
You look at the at the gap under the closed door for any light as you flip away... then you have 2 chances out of 3 to get the prize (...or is that another brain teaser ?).
Or maybe you remove the cover plate over the switches and pull out the wires a bit, then you haul out your trusty amprobe and see which one draws current when flipped on.
Or how about turning them on one at a time and each time go outside and look at the watthour meter to see if it's turning faster...
(enough already ?)
11-27-2001, 09:18 PM
Start with all the switches in the OFF position for a long time. Turn switch #1 ON and switch #2 ON. Wait five minutes. Then turn switch #2 OFF. Wait one minute. Then, quickly turn switch #1 OFF and #4 ON and rush into the room and grab the bulb (using the same calibrated fingers you use for measuring discharge temperatures). If the bulb is hot (but unlit), switch #1 controls the lamp. If the bulb is lukewarm (but unlit), switch #2 controls the lamp. If the bulb is cold (but unlit), switch #3 controls the lamp. If the lamp is lit, switch #4 controls the lamp.
" You thank you bad don't you". Not the most accurate but there's more than one way to skin a cat.
Switches 3 and 4 on for 15 min or so.
Then turn 3 off and 2 on, enter room.
Dark and cool= sw-1
Bright and cool= sw-2
Dark and warm = sw-3
Bright and warm = sw-4
11-28-2001, 01:22 PM
...cehs solution is the best (it's faster). It is no surprise he thought of it first.
That was another great brain-teaser. Very creative. You've got great material, nate.
I agree, these are new and fun. Keep 'em coming!
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