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Wednesday, June 11, 2014

3 bulbs 3 switches puzzle with LED bulbs

Here's the puzzle.
There are three light switches up in the attic of an old house. They control three light bulbs down in the basement. The problem is that you don't know which switch is connected to which bulb. You can make one trip down to the basement to figure this out. How are you going to do it?

Think and you'll easily come up with the traditional answer that's applicable to incandescent bulbs.

Don't know?

The answer that's expected is: Switch on one bulb for a long time, then switch it off, switch another on, and go to the basement immediately. The bulb shining has the second switch. And the warmer of the two unlit bulbs has the first switch.

What if the bulbs were made of LEDs?

Since the question isn't serious, I came up with two solutions of my own - which may or may not answer the question correctly. For educational purpose, they are:

1) Use an arduino to make one LED blink. Switch one on, keep one off. Go to basement and correlate the bulbs.
2) LEDs can emit light as well as detect light. So, if the bulbs are not arranged in an equilateral triangle fashion, switch one on, and measure the multimeter readings in the other two switches. Then go to the basement. The bulb closer to the shining bulb has the switch which showed the larger multimeter reading.

Flaws and other solutions are welcome.
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Drop me a comment if anything is missing


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